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Refine the change in r52258 for avoiding use-before-def conditions

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when changing the stride of a comparison so that it's slightly
more precise, by having it scan the instruction list to determine
if there is a use of the condition after the point where the
condition will be inserted.

llvm-svn: 52371
This commit is contained in:
Dan Gohman 2008-06-16 22:34:15 +00:00
parent dd707dc82d
commit c1fd5f170b
3 changed files with 43 additions and 12 deletions
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21
lib/Transforms/Scalar/LoopStrengthReduce.cpp
View File

@ -1530,15 +1530,6 @@ namespace {
ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
IVStrideUse* &CondUse,
const SCEVHandle* &CondStride) {
// Forgo this transformation if the condition has multiple uses. This is
// over-conservative, but simpler than alternatives. It guards against
// comparisons with a use that occurs earlier than the add instruction for the
// new stride index. See
// test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll
// for an example of this situation.
if (!Cond->hasOneUse())
return Cond;
if (StrideOrder.size() < 2 ||
IVUsesByStride[*CondStride].Users.size() != 1)
return Cond;
@ -1653,6 +1644,18 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
}
}
// Forgo this transformation if it the increment happens to be
// unfortunately positioned after the condition, and the condition
// has multiple uses which prevent it from being moved immediately
// before the branch. See
// test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-*.ll
// for an example of this situation.
if (!Cond->hasOneUse())
for (BasicBlock::iterator I = Cond, E = Cond->getParent()->end();
I != E; ++I)
if (I == NewIncV)
return Cond;
if (NewCmpVal != CmpVal) {
// Create a new compare instruction using new stride / iv.
ICmpInst *OldCond = Cond;

24
test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-0.ll Normal file
View File

@ -0,0 +1,24 @@
; RUN: llvm-as < %s | llc --x86-asm-syntax=att | grep {cmpl \$4}
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-apple-darwin9"
; This is like change-compare-stride-trickiness-1.ll except the comparison
; happens before the relevant use, so the comparison stride can't be
; easily changed.
define void @foo() {
entry:
br label %loop
loop:
%indvar = phi i32 [ 0, %entry ], [ %i.2.0.us1534, %loop ] ; <i32> [#uses=1]
%i.2.0.us1534 = add i32 %indvar, 1 ; <i32> [#uses=3]
%tmp611.us1535 = icmp eq i32 %i.2.0.us1534, 4 ; <i1> [#uses=2]
%tmp623.us1538 = select i1 %tmp611.us1535, i32 6, i32 0 ; <i32> [#uses=0]
%tmp628.us1540 = shl i32 %i.2.0.us1534, 1 ; <i32> [#uses=1]
%tmp645646647.us1547 = sext i32 %tmp628.us1540 to i64 ; <i64> [#uses=0]
br i1 %tmp611.us1535, label %exit, label %loop
exit:
ret void
}

10
test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness.ll → test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-1.ll
View File

@ -1,7 +1,11 @@
; RUN: llvm-as < %s | llc
; RUN: llvm-as < %s | llc --x86-asm-syntax=att | grep {cmpl \$8}
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
target triple = "x86_64-apple-darwin9"
; This is like change-compare-stride-trickiness-0.ll except the comparison
; happens after the relevant use, so the comparison stride can be
; easily changed.
define void @foo() {
entry:
br label %loop
@ -9,10 +13,10 @@ entry:
loop:
%indvar = phi i32 [ 0, %entry ], [ %i.2.0.us1534, %loop ] ; <i32> [#uses=1]
%i.2.0.us1534 = add i32 %indvar, 1 ; <i32> [#uses=3]
%tmp611.us1535 = icmp eq i32 %i.2.0.us1534, 4 ; <i1> [#uses=2]
%tmp623.us1538 = select i1 %tmp611.us1535, i32 6, i32 0 ; <i32> [#uses=0]
%tmp628.us1540 = shl i32 %i.2.0.us1534, 1 ; <i32> [#uses=1]
%tmp645646647.us1547 = sext i32 %tmp628.us1540 to i64 ; <i64> [#uses=0]
%tmp611.us1535 = icmp eq i32 %i.2.0.us1534, 4 ; <i1> [#uses=2]
%tmp623.us1538 = select i1 %tmp611.us1535, i32 6, i32 0 ; <i32> [#uses=0]
br i1 %tmp611.us1535, label %exit, label %loop
exit: