[llvm] r278584 - [IndVars] Ignore (s|z)exts that don't extend the induction variable
Sanjoy Das via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 12 17:58:31 PDT 2016
Author: sanjoy
Date: Fri Aug 12 19:58:31 2016
New Revision: 278584
URL: http://llvm.org/viewvc/llvm-project?rev=278584&view=rev
Log:
[IndVars] Ignore (s|z)exts that don't extend the induction variable
`IVVisitor::visitCast` used to have the invariant that if the
instruction it was passed was a sext or zext instruction, the result of
the instruction would be wider than the induction variable. This is no
longer true after rL275037, so this change teaches `IndVarSimplify` s
implementation of `IVVisitor::visitCast` to work with the relaxed
invariant.
A corresponding change to SimplifyIndVar to preserve the said invariant
after rL275037 would also work, but given how `IVVisitor::visitCast` is
spelled (no indication of said invariant), I figured the current fix is
cleaner.
Fixes PR28935.
Added:
llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=278584&r1=278583&r2=278584&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Fri Aug 12 19:58:31 2016
@@ -816,6 +816,14 @@ static void visitIVCast(CastInst *Cast,
if (!Cast->getModule()->getDataLayout().isLegalInteger(Width))
return;
+ // Check that `Cast` actually extends the induction variable (we rely on this
+ // later). This takes care of cases where `Cast` is extending a truncation of
+ // the narrow induction variable, and thus can end up being narrower than the
+ // "narrow" induction variable.
+ uint64_t NarrowIVWidth = SE->getTypeSizeInBits(WI.NarrowIV->getType());
+ if (NarrowIVWidth >= Width)
+ return;
+
// Cast is either an sext or zext up to this point.
// We should not widen an indvar if arithmetics on the wider indvar are more
// expensive than those on the narrower indvar. We check only the cost of ADD
Added: llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll?rev=278584&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll (added)
+++ llvm/trunk/test/Transforms/IndVarSimplify/pr28935.ll Fri Aug 12 19:58:31 2016
@@ -0,0 +1,20 @@
+; RUN: opt -S -indvars < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare i16 @fn1(i16 returned, i64)
+
+define void @fn2() {
+; CHECK-LABEL: @fn2(
+entry:
+ br label %for.cond
+
+for.cond:
+ %f.0 = phi i64 [ undef, %entry ], [ %inc, %for.cond ]
+ %conv = trunc i64 %f.0 to i16
+ %call = tail call i16 @fn1(i16 %conv, i64 %f.0)
+ %conv2 = zext i16 %call to i32
+ %inc = add nsw i64 %f.0, 1
+ br label %for.cond
+}
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