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The DAGCombiner was threading select over pairs of extending loads even

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if the extension types were not the same.  The result was that if you
fed a select with sext and zext loads, as in the testcase, then it
would get turned into a zext (or sext) of the select, which is wrong
in the cases when it should have been an sext (resp. zext).  Reported
and diagnosed by Sebastien Deldon.

llvm-svn: 119728
This commit is contained in:
Duncan Sands 2010-11-18 20:05:18 +00:00
parent 4562d3b919
commit a61bc1a41a
2 changed files with 20 additions and 0 deletions
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5
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -6658,6 +6658,11 @@ bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
LLD->isVolatile() || RLD->isVolatile() ||
// If this is an EXTLOAD, the VT's must match.
LLD->getMemoryVT() != RLD->getMemoryVT() ||
// If this is an EXTLOAD, the kind of extension must match.
(LLD->getExtensionType() != RLD->getExtensionType() &&
// The only exception is if one of the extensions is anyext.
LLD->getExtensionType() != ISD::EXTLOAD &&
RLD->getExtensionType() != ISD::EXTLOAD) ||
// FIXME: this discards src value information. This is
// over-conservative. It would be beneficial to be able to remember
// both potential memory locations. Since we are discarding

15
test/CodeGen/X86/2010-11-18-SelectOfExtload.ll Normal file
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@ -0,0 +1,15 @@
; RUN: llc < %s -march=x86 | FileCheck %s
; Both values were being zero extended.
@u = external global i8
@s = external global i8
define i32 @foo(i1 %cond) {
; CHECK: @foo
%u_base = load i8* @u
%u_val = zext i8 %u_base to i32
; CHECK: movzbl
; CHECK: movsbl
%s_base = load i8* @s
%s_val = sext i8 %s_base to i32
%val = select i1 %cond, i32 %u_val, i32 %s_val
ret i32 %val
}