RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-24 19:52:54 +01:00
Code Issues Projects Releases Wiki Activity

fix a bug (possibly 8816) in the sadd forming xform: it isn't

Browse Source 
profitable (or safe) to promote code when the add-with-constant
has other uses.

llvm-svn: 122175
This commit is contained in:
Chris Lattner 2010-12-19 17:59:02 +00:00
parent cc804862d5
commit c7876edb16
2 changed files with 39 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1588,6 +1588,16 @@ Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) {
static Instruction *ProcessUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B,
ConstantInt *CI2, ConstantInt *CI1,
InstCombiner::BuilderTy *Builder) {
// The transformation we're trying to do here is to transform this into an
// llvm.sadd.with.overflow. To do this, we have to replace the original add
// with a narrower add, and discard the add-with-constant that is part of the
// range check (if we can't eliminate it, this isn't profitable).
// In order to eliminate the add-with-constant, the compare can be its only
// use.
Value *AddWithCst = I.getOperand(0);
if (!AddWithCst->hasOneUse()) return 0;
const IntegerType *WideType = cast<IntegerType>(CI1->getType());
unsigned WideWidth = WideType->getBitWidth();
unsigned NarrowWidth = WideWidth / 2;

30
test/Transforms/InstCombine/overflow.ll
View File

@ -1,6 +1,8 @@
; RUN: opt -S -instcombine < %s | FileCheck %s
; <rdar://problem/8558713>
declare i32 @throwAnExceptionOrWhatever(...)
; CHECK: @test1
define i32 @test1(i32 %a, i32 %b) nounwind ssp {
entry:
@ -24,4 +26,30 @@ if.end:
ret i32 %conv9
}
declare i32 @throwAnExceptionOrWhatever(...)
; CHECK: @test2
; This form should not be promoted for two reasons: 1) it is unprofitable to
; promote it since the add.off instruction has another use, and 2) it is unsafe
; because the add-with-off makes the high bits of the original add live.
define i32 @test2(i32 %a, i32 %b, i64* %P) nounwind ssp {
entry:
%conv = sext i32 %a to i64
%conv2 = sext i32 %b to i64
%add = add nsw i64 %conv2, %conv
%add.off = add i64 %add, 2147483648
store i64 %add.off, i64* %P
; CHECK-NOT: llvm.sadd.with.overflow
%0 = icmp ugt i64 %add.off, 4294967295
br i1 %0, label %if.then, label %if.end
if.then:
%call = tail call i32 (...)* @throwAnExceptionOrWhatever() nounwind
br label %if.end
if.end:
%conv9 = trunc i64 %add to i32
; CHECK: ret i32
ret i32 %conv9
}