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[IndVars] Remove unreasonable checks in rewriteLoopExitValues

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A piece of logic in rewriteLoopExitValues has a weird check on number of
users which allowed an unprofitable transform in case if an instruction has
more than 6 users.

Differential Revision: https://reviews.llvm.org/D51404
Reviewed By: etherzhhb

llvm-svn: 342444
This commit is contained in:
Max Kazantsev 2018-09-18 04:57:18 +00:00
parent ebf46143ea
commit 0994abda3a
2 changed files with 35 additions and 11 deletions
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16
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -603,12 +603,9 @@ bool IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
if (ExitValue->getSCEVType()>=scMulExpr) {
bool HasHardInternalUses = false;
bool HasSoftExternalUses = false;
unsigned NumUses = 0;
for (auto IB = Inst->user_begin(), IE = Inst->user_end();
IB != IE && NumUses <= 6; ++IB) {
Instruction *UseInstr = cast<Instruction>(*IB);
for (auto *IB : Inst->users()) {
Instruction *UseInstr = cast<Instruction>(IB);
unsigned Opc = UseInstr->getOpcode();
NumUses++;
if (L->contains(UseInstr)) {
if (Opc == Instruction::Call)
HasHardInternalUses = true;
@ -616,11 +613,8 @@ bool IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
if (Opc == Instruction::PHI) {
// Do not count the Phi as a use. LCSSA may have inserted
// plenty of trivial ones.
NumUses--;
for (auto PB = UseInstr->user_begin(),
PE = UseInstr->user_end();
PB != PE && NumUses <= 6; ++PB, ++NumUses) {
unsigned PhiOpc = cast<Instruction>(*PB)->getOpcode();
for (auto *PB : UseInstr->users()) {
unsigned PhiOpc = cast<Instruction>(PB)->getOpcode();
if (PhiOpc != Instruction::Call &&
PhiOpc != Instruction::Ret) {
HasSoftExternalUses = true;
@ -635,7 +629,7 @@ bool IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
}
}
}
if (NumUses <= 6 && HasHardInternalUses && !HasSoftExternalUses)
if (HasHardInternalUses && !HasSoftExternalUses)
continue;
}

30
llvm/test/Transforms/IndVarSimplify/dont-recompute.ll
View File

@ -67,3 +67,33 @@ for.end: ; preds = %for.body
; CHECK-NEXT: ret i32 %add.lcssa
ret i32 %add
}
; CHECK-LABEL: @test3(
define void @test3(i32 %m) nounwind uwtable {
entry:
br label %for.body
for.body: ; preds = %for.body, %entry
%i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%a.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
%add = add i32 %a.05, %m
mul i32 %add, 1
mul i32 %add, 1
mul i32 %add, 1
mul i32 %add, 1
mul i32 %add, 1
mul i32 %add, 1
; CHECK: tail call void @func(i32 %add)
tail call void @func(i32 %add)
%inc = add nsw i32 %i.06, 1
%exitcond = icmp eq i32 %inc, 186
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body
; CHECK: for.end:
; CHECK-NOT: mul i32 %m, 186
; CHECK:%add.lcssa = phi i32 [ %add, %for.body ]
; CHECK-NEXT: tail call void @func(i32 %add.lcssa)
tail call void @func(i32 %add)
ret void
}