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Use SimplifyDemandedBits on div instructions. 

This folds away silly stuff like (a&255)/1000 -> 0.

llvm-svn: 130614
This commit is contained in:
Benjamin Kramer 2011-04-30 18:16:00 +00:00
parent 6a50bbd284
commit 57b3df59b9
2 changed files with 11 additions and 0 deletions
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4
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -320,6 +320,10 @@ Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) {
} }
} }
// See if we can fold away this div instruction.
if (SimplifyDemandedInstructionBits(I))
return &I;
// (X - (X rem Y)) / Y -> X / Y; usually originates as ((X / Y) * Y) / Y // (X - (X rem Y)) / Y -> X / Y; usually originates as ((X / Y) * Y) / Y
Value *X = 0, *Z = 0; Value *X = 0, *Z = 0;
if (match(Op0, m_Sub(m_Value(X), m_Value(Z)))) { // (X - Z) / Y; Y = Op1 if (match(Op0, m_Sub(m_Value(X), m_Value(Z)))) { // (X - Z) / Y; Y = Op1

7
llvm/test/Transforms/InstCombine/div.ll
View File

@ -111,3 +111,10 @@ define i32 @test13(i32 %x) nounwind {
; CHECK-NEXT: ret i32 1 ; CHECK-NEXT: ret i32 1
} }
define i32 @test14(i8 %x) nounwind {
%zext = zext i8 %x to i32
%div = udiv i32 %zext, 257 ; 0
ret i32 %div
; CHECK: @test14
; CHECK-NEXT: ret i32 0
}