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Extend trip count instead of truncating IV in LFTR, when legal
When legal, extending trip count in the loop control logic generates better code compared to truncating IV. This is because (1) extending trip count is a loop invariant operation (see genLoopLimit where we prove trip count is loop invariant). (2) Scalar Evolution seems to have problems understanding trunc when computing loop trip count. So removing them allows better analysis performed in Scalar Evolution. (In particular this fixes PR 28363 which is the motivation for this change). I am not going to perform any performance test. Any degradation caused by this should be an indication of a bug elsewhere. To prove legality, we rely on SCEV to prove zext(trunc(IV)) == IV (or similarly for sext). If this holds, we can prove equivalence of trunc(IV)==ExitCnt (1) and IV == zext(ExitCnt). Simply take zext of boths sides of (1) and apply the proven equivalence. https://reviews.llvm.org/D23075 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278334 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ehsan Amiri
parent
3876e2e984
commit
543fef7ea9
@ -1989,8 +1989,36 @@ linearFunctionTestReplace(Loop *L,
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DEBUG(dbgs() << " Widen RHS:\t" << *ExitCnt << "\n");
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} else {
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CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
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"lftr.wideiv");
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// We try to extend trip count first. If that doesn't work we truncate IV.
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// Zext(trunc(IV)) == IV implies equivalence of the following two:
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// Trunc(IV) == ExitCnt and IV == zext(ExitCnt). Similarly for sext. If
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// one of the two holds, extend the trip count, otherwise truncate IV.
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bool Extended = false;
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const SCEV *IV = SE->getSCEV(CmpIndVar);
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const SCEV *ZExtTrunc =
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SE->getZeroExtendExpr(SE->getTruncateExpr(SE->getSCEV(CmpIndVar),
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ExitCnt->getType()),
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CmpIndVar->getType());
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if (ZExtTrunc == IV) {
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Extended = true;
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ExitCnt = Builder.CreateZExt(ExitCnt, IndVar->getType(),
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"wide.trip.count");
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} else {
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const SCEV *SExtTrunc =
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SE->getSignExtendExpr(SE->getTruncateExpr(SE->getSCEV(CmpIndVar),
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ExitCnt->getType()),
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CmpIndVar->getType());
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if (SExtTrunc == IV) {
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Extended = true;
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ExitCnt = Builder.CreateSExt(ExitCnt, IndVar->getType(),
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"wide.trip.count");
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}
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}
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if (!Extended)
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CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(),
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"lftr.wideiv");
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}
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}
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Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond");
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@ -41,6 +41,8 @@ entry:
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br i1 %precond, label %loop, label %return
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; CHECK: loop:
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; CHECK-NOT: sext
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; CHECK: wide.trip.count = sext
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; CHECK-NOT: sext
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; CHECK: exit:
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loop:
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%iv = phi i32 [ %postiv, %loop ], [ %init, %entry ]
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158
test/Transforms/IndVarSimplify/lftr-wide-trip-count.ll
Normal file
158
test/Transforms/IndVarSimplify/lftr-wide-trip-count.ll
Normal file
@ -0,0 +1,158 @@
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; RUN: opt -S -indvars < %s | FileCheck %s
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; Provide legal integer types.
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target datalayout = "n8:16:32:64"
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define void @test1(float* %autoc,
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float* %data,
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float %d, i32 %data_len, i32 %sample) nounwind {
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entry:
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%sub = sub i32 %data_len, %sample
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%cmp4 = icmp eq i32 %data_len, %sample
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br i1 %cmp4, label %for.end, label %for.body
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for.body: ; preds = %entry, %for.body
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%indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 68719476736, %entry ]
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%temp = trunc i64 %indvars.iv to i32
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%add = add i32 %temp, %sample
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%idxprom = zext i32 %add to i64
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%arrayidx = getelementptr inbounds float, float* %data, i64 %idxprom
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%temp1 = load float, float* %arrayidx, align 4
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%mul = fmul float %temp1, %d
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%arrayidx2 = getelementptr inbounds float, float* %autoc, i64 %indvars.iv
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%temp2 = load float, float* %arrayidx2, align 4
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%add3 = fadd float %temp2, %mul
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store float %add3, float* %arrayidx2, align 4
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%indvars.iv.next = add i64 %indvars.iv, 1
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%temp3 = trunc i64 %indvars.iv.next to i32
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%cmp = icmp ult i32 %temp3, %sub
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br i1 %cmp, label %for.body, label %for.end
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for.end: ; preds = %for.body, %entry
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ret void
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; CHECK-LABEL: @test1(
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; With the given initial value for IV, it is not legal to widen
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; trip count to IV size
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; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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; CHECK: %lftr.wideiv = trunc i64 %indvars.iv.next to i32
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; CHECK: %exitcond = icmp ne i32 %lftr.wideiv, %sub
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; CHECK: br i1 %exitcond, label %for.body, label %for.end.loopexit
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}
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define float @test2(float* %a,
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float* %b,
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i32 zeroext %m) local_unnamed_addr #0 {
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entry:
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%cmp5 = icmp ugt i32 %m, 500
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br i1 %cmp5, label %for.body.preheader, label %for.end
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for.body.preheader: ; preds = %entry
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br label %for.body
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for.body: ; preds = %for.body.preheader, %for.body
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%sum.07 = phi float [ %add, %for.body ], [ 0.000000e+00, %for.body.preheader ]
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%i.06 = phi i32 [ %inc, %for.body ], [ 500, %for.body.preheader ]
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%idxprom = zext i32 %i.06 to i64
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%arrayidx = getelementptr inbounds float, float* %b, i64 %idxprom
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%temp = load float, float* %arrayidx, align 4
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%arrayidx2 = getelementptr inbounds float, float* %a, i64 %idxprom
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%temp1 = load float, float* %arrayidx2, align 4
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%mul = fmul float %temp, %temp1
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%add = fadd float %sum.07, %mul
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%inc = add i32 %i.06, 1
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%cmp = icmp ult i32 %inc, %m
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br i1 %cmp, label %for.body, label %for.end.loopexit
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for.end.loopexit: ; preds = %for.body
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br label %for.end
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for.end: ; preds = %for.end.loopexit, %entry
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%sum.0.lcssa = phi float [ 0.000000e+00, %entry ], [ %add, %for.end.loopexit ]
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ret float %sum.0.lcssa
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; CHECK-LABEL: @test2(
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; Trip count should be widened and LFTR should canonicalize the condition
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; CHECK: %wide.trip.count = zext
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; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count
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; CHECK: br i1 %exitcond
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}
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define float @test3(float* %b,
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i32 signext %m) local_unnamed_addr #0 {
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entry:
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%cmp5 = icmp sgt i32 %m, -10
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br i1 %cmp5, label %for.body.preheader, label %for.end
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for.body.preheader: ; preds = %entry
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br label %for.body
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for.body: ; preds = %for.body.preheader, %for.body
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%sum.07 = phi float [ %add1, %for.body ], [ 0.000000e+00, %for.body.preheader ]
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%i.06 = phi i32 [ %inc, %for.body ], [ -10, %for.body.preheader ]
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%add = add nsw i32 %i.06, 20
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%idxprom = sext i32 %add to i64
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%arrayidx = getelementptr inbounds float, float* %b, i64 %idxprom
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%temp = load float, float* %arrayidx, align 4
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%conv = sitofp i32 %i.06 to float
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%mul = fmul float %conv, %temp
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%add1 = fadd float %sum.07, %mul
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%inc = add nsw i32 %i.06, 1
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%cmp = icmp slt i32 %inc, %m
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br i1 %cmp, label %for.body, label %for.end.loopexit
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for.end.loopexit: ; preds = %for.body
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br label %for.end
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for.end: ; preds = %for.end.loopexit, %entry
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%sum.0.lcssa = phi float [ 0.000000e+00, %entry ], [ %add1, %for.end.loopexit ]
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ret float %sum.0.lcssa
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; CHECK-LABEL: @test3(
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; Trip count should be widened and LFTR should canonicalize the condition
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; CHECK: %wide.trip.count = sext
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; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count
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; CHECK: br i1 %exitcond
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}
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define float @test4(float* %b,
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i32 signext %m) local_unnamed_addr #0 {
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entry:
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%cmp5 = icmp sgt i32 %m, 10
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br i1 %cmp5, label %for.body.preheader, label %for.end
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for.body.preheader: ; preds = %entry
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br label %for.body
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for.body: ; preds = %for.body.preheader, %for.body
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%sum.07 = phi float [ %add1, %for.body ], [ 0.000000e+00, %for.body.preheader ]
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%i.06 = phi i32 [ %inc, %for.body ], [ 10, %for.body.preheader ]
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%add = add nsw i32 %i.06, 20
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%idxprom = sext i32 %add to i64
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%arrayidx = getelementptr inbounds float, float* %b, i64 %idxprom
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%temp = load float, float* %arrayidx, align 4
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%conv = sitofp i32 %i.06 to float
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%mul = fmul float %conv, %temp
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%add1 = fadd float %sum.07, %mul
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%inc = add nsw i32 %i.06, 1
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%cmp = icmp slt i32 %inc, %m
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br i1 %cmp, label %for.body, label %for.end.loopexit
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for.end.loopexit: ; preds = %for.body
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%add1.lcssa = phi float [ %add1, %for.body ]
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br label %for.end
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for.end: ; preds = %for.end.loopexit, %entry
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%sum.0.lcssa = phi float [ 0.000000e+00, %entry ], [ %add1.lcssa, %for.end.loopexit ]
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ret float %sum.0.lcssa
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; CHECK-LABEL: @test4(
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; Trip count should be widened and LFTR should canonicalize the condition
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; CHECK: %wide.trip.count = zext
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; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count
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; CHECK: br i1 %exitcond
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}
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@ -33,8 +33,9 @@ for.end: ; preds = %for.body, %entry
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; CHECK-LABEL: @test1(
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; check that we turn the IV test into an eq.
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; CHECK: %lftr.wideiv = trunc i64 %indvars.iv.next to i32
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; CHECK: %exitcond = icmp ne i32 %lftr.wideiv, %sub
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; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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; CHECK: %wide.trip.count = zext i32 %sub to i64
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; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count
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; CHECK: br i1 %exitcond, label %for.body, label %for.end.loopexit
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}
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