From 543fef7ea9f1be9adadb039a3f55d5a2fd79510a Mon Sep 17 00:00:00 2001 From: Ehsan Amiri Date: Thu, 11 Aug 2016 13:51:20 +0000 Subject: [PATCH] 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 --- lib/Transforms/Scalar/IndVarSimplify.cpp | 32 +++- test/Transforms/IndVarSimplify/elim-extend.ll | 2 + .../IndVarSimplify/lftr-wide-trip-count.ll | 158 ++++++++++++++++++ .../IndVarSimplify/ult-sub-to-eq.ll | 5 +- 4 files changed, 193 insertions(+), 4 deletions(-) create mode 100644 test/Transforms/IndVarSimplify/lftr-wide-trip-count.ll diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp index 4cb2d0d1bf9..ddd5cdc6bcc 100644 --- a/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -1989,8 +1989,36 @@ linearFunctionTestReplace(Loop *L, DEBUG(dbgs() << " Widen RHS:\t" << *ExitCnt << "\n"); } else { - CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(), - "lftr.wideiv"); + // We try to extend trip count first. If that doesn't work we truncate IV. + // Zext(trunc(IV)) == IV implies equivalence of the following two: + // Trunc(IV) == ExitCnt and IV == zext(ExitCnt). Similarly for sext. If + // one of the two holds, extend the trip count, otherwise truncate IV. + bool Extended = false; + const SCEV *IV = SE->getSCEV(CmpIndVar); + const SCEV *ZExtTrunc = + SE->getZeroExtendExpr(SE->getTruncateExpr(SE->getSCEV(CmpIndVar), + ExitCnt->getType()), + CmpIndVar->getType()); + + if (ZExtTrunc == IV) { + Extended = true; + ExitCnt = Builder.CreateZExt(ExitCnt, IndVar->getType(), + "wide.trip.count"); + } else { + const SCEV *SExtTrunc = + SE->getSignExtendExpr(SE->getTruncateExpr(SE->getSCEV(CmpIndVar), + ExitCnt->getType()), + CmpIndVar->getType()); + if (SExtTrunc == IV) { + Extended = true; + ExitCnt = Builder.CreateSExt(ExitCnt, IndVar->getType(), + "wide.trip.count"); + } + } + + if (!Extended) + CmpIndVar = Builder.CreateTrunc(CmpIndVar, ExitCnt->getType(), + "lftr.wideiv"); } } Value *Cond = Builder.CreateICmp(P, CmpIndVar, ExitCnt, "exitcond"); diff --git a/test/Transforms/IndVarSimplify/elim-extend.ll b/test/Transforms/IndVarSimplify/elim-extend.ll index 8daac23ea74..6b6d5974165 100644 --- a/test/Transforms/IndVarSimplify/elim-extend.ll +++ b/test/Transforms/IndVarSimplify/elim-extend.ll @@ -41,6 +41,8 @@ entry: br i1 %precond, label %loop, label %return ; CHECK: loop: ; CHECK-NOT: sext +; CHECK: wide.trip.count = sext +; CHECK-NOT: sext ; CHECK: exit: loop: %iv = phi i32 [ %postiv, %loop ], [ %init, %entry ] diff --git a/test/Transforms/IndVarSimplify/lftr-wide-trip-count.ll b/test/Transforms/IndVarSimplify/lftr-wide-trip-count.ll new file mode 100644 index 00000000000..25c91ddef81 --- /dev/null +++ b/test/Transforms/IndVarSimplify/lftr-wide-trip-count.ll @@ -0,0 +1,158 @@ +; RUN: opt -S -indvars < %s | FileCheck %s + +; Provide legal integer types. +target datalayout = "n8:16:32:64" + + +define void @test1(float* %autoc, + float* %data, + float %d, i32 %data_len, i32 %sample) nounwind { +entry: + %sub = sub i32 %data_len, %sample + %cmp4 = icmp eq i32 %data_len, %sample + br i1 %cmp4, label %for.end, label %for.body + +for.body: ; preds = %entry, %for.body + %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 68719476736, %entry ] + %temp = trunc i64 %indvars.iv to i32 + %add = add i32 %temp, %sample + %idxprom = zext i32 %add to i64 + %arrayidx = getelementptr inbounds float, float* %data, i64 %idxprom + %temp1 = load float, float* %arrayidx, align 4 + %mul = fmul float %temp1, %d + %arrayidx2 = getelementptr inbounds float, float* %autoc, i64 %indvars.iv + %temp2 = load float, float* %arrayidx2, align 4 + %add3 = fadd float %temp2, %mul + store float %add3, float* %arrayidx2, align 4 + %indvars.iv.next = add i64 %indvars.iv, 1 + %temp3 = trunc i64 %indvars.iv.next to i32 + %cmp = icmp ult i32 %temp3, %sub + br i1 %cmp, label %for.body, label %for.end + +for.end: ; preds = %for.body, %entry + ret void + +; CHECK-LABEL: @test1( + +; With the given initial value for IV, it is not legal to widen +; trip count to IV size +; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1 +; CHECK: %lftr.wideiv = trunc i64 %indvars.iv.next to i32 +; CHECK: %exitcond = icmp ne i32 %lftr.wideiv, %sub +; CHECK: br i1 %exitcond, label %for.body, label %for.end.loopexit +} + +define float @test2(float* %a, + float* %b, + i32 zeroext %m) local_unnamed_addr #0 { +entry: + %cmp5 = icmp ugt i32 %m, 500 + br i1 %cmp5, label %for.body.preheader, label %for.end + +for.body.preheader: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.preheader, %for.body + %sum.07 = phi float [ %add, %for.body ], [ 0.000000e+00, %for.body.preheader ] + %i.06 = phi i32 [ %inc, %for.body ], [ 500, %for.body.preheader ] + %idxprom = zext i32 %i.06 to i64 + %arrayidx = getelementptr inbounds float, float* %b, i64 %idxprom + %temp = load float, float* %arrayidx, align 4 + %arrayidx2 = getelementptr inbounds float, float* %a, i64 %idxprom + %temp1 = load float, float* %arrayidx2, align 4 + %mul = fmul float %temp, %temp1 + %add = fadd float %sum.07, %mul + %inc = add i32 %i.06, 1 + %cmp = icmp ult i32 %inc, %m + br i1 %cmp, label %for.body, label %for.end.loopexit + +for.end.loopexit: ; preds = %for.body + br label %for.end + +for.end: ; preds = %for.end.loopexit, %entry + %sum.0.lcssa = phi float [ 0.000000e+00, %entry ], [ %add, %for.end.loopexit ] + ret float %sum.0.lcssa + +; CHECK-LABEL: @test2( +; Trip count should be widened and LFTR should canonicalize the condition +; CHECK: %wide.trip.count = zext +; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count +; CHECK: br i1 %exitcond +} + +define float @test3(float* %b, + i32 signext %m) local_unnamed_addr #0 { +entry: + %cmp5 = icmp sgt i32 %m, -10 + br i1 %cmp5, label %for.body.preheader, label %for.end + +for.body.preheader: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.preheader, %for.body + %sum.07 = phi float [ %add1, %for.body ], [ 0.000000e+00, %for.body.preheader ] + %i.06 = phi i32 [ %inc, %for.body ], [ -10, %for.body.preheader ] + %add = add nsw i32 %i.06, 20 + %idxprom = sext i32 %add to i64 + %arrayidx = getelementptr inbounds float, float* %b, i64 %idxprom + %temp = load float, float* %arrayidx, align 4 + %conv = sitofp i32 %i.06 to float + %mul = fmul float %conv, %temp + %add1 = fadd float %sum.07, %mul + %inc = add nsw i32 %i.06, 1 + %cmp = icmp slt i32 %inc, %m + br i1 %cmp, label %for.body, label %for.end.loopexit + +for.end.loopexit: ; preds = %for.body + br label %for.end + +for.end: ; preds = %for.end.loopexit, %entry + %sum.0.lcssa = phi float [ 0.000000e+00, %entry ], [ %add1, %for.end.loopexit ] + ret float %sum.0.lcssa + +; CHECK-LABEL: @test3( +; Trip count should be widened and LFTR should canonicalize the condition +; CHECK: %wide.trip.count = sext +; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count +; CHECK: br i1 %exitcond +} + +define float @test4(float* %b, + i32 signext %m) local_unnamed_addr #0 { +entry: + %cmp5 = icmp sgt i32 %m, 10 + br i1 %cmp5, label %for.body.preheader, label %for.end + +for.body.preheader: ; preds = %entry + br label %for.body + +for.body: ; preds = %for.body.preheader, %for.body + %sum.07 = phi float [ %add1, %for.body ], [ 0.000000e+00, %for.body.preheader ] + %i.06 = phi i32 [ %inc, %for.body ], [ 10, %for.body.preheader ] + %add = add nsw i32 %i.06, 20 + %idxprom = sext i32 %add to i64 + %arrayidx = getelementptr inbounds float, float* %b, i64 %idxprom + %temp = load float, float* %arrayidx, align 4 + %conv = sitofp i32 %i.06 to float + %mul = fmul float %conv, %temp + %add1 = fadd float %sum.07, %mul + %inc = add nsw i32 %i.06, 1 + %cmp = icmp slt i32 %inc, %m + br i1 %cmp, label %for.body, label %for.end.loopexit + +for.end.loopexit: ; preds = %for.body + %add1.lcssa = phi float [ %add1, %for.body ] + br label %for.end + +for.end: ; preds = %for.end.loopexit, %entry + %sum.0.lcssa = phi float [ 0.000000e+00, %entry ], [ %add1.lcssa, %for.end.loopexit ] + ret float %sum.0.lcssa + +; CHECK-LABEL: @test4( +; Trip count should be widened and LFTR should canonicalize the condition +; CHECK: %wide.trip.count = zext +; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count +; CHECK: br i1 %exitcond +} + + diff --git a/test/Transforms/IndVarSimplify/ult-sub-to-eq.ll b/test/Transforms/IndVarSimplify/ult-sub-to-eq.ll index 30dcbf50088..6a7e5b70ca1 100644 --- a/test/Transforms/IndVarSimplify/ult-sub-to-eq.ll +++ b/test/Transforms/IndVarSimplify/ult-sub-to-eq.ll @@ -33,8 +33,9 @@ for.end: ; preds = %for.body, %entry ; CHECK-LABEL: @test1( ; check that we turn the IV test into an eq. -; CHECK: %lftr.wideiv = trunc i64 %indvars.iv.next to i32 -; CHECK: %exitcond = icmp ne i32 %lftr.wideiv, %sub +; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1 +; CHECK: %wide.trip.count = zext i32 %sub to i64 +; CHECK: %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count ; CHECK: br i1 %exitcond, label %for.body, label %for.end.loopexit }