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[SCEV] Canonicalize "A /u C1 /u C2" to "A /u (C1*C2)". 

Summary: FWIW InstCombine already folds this. Also avoid the case where C1*C2 overflows.

Reviewers: sunfish, sanjoy

Subscribers: hiraditya, bixia, llvm-commits

Differential Revision: https://reviews.llvm.org/D47965

llvm-svn: 334425
This commit is contained in:
Tim Shen 2018-06-11 18:44:58 +00:00
parent 789494026e
commit cc63761720
2 changed files with 43 additions and 0 deletions
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15
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -3066,6 +3066,21 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
}
}
}
// (A/B)/C --> A/(B*C) if safe and B*C can be folded.
if (const SCEVUDivExpr *OtherDiv = dyn_cast<SCEVUDivExpr>(LHS)) {
if (auto *DivisorConstant =
dyn_cast<SCEVConstant>(OtherDiv->getRHS())) {
bool Overflow = false;
APInt NewRHS =
DivisorConstant->getAPInt().umul_ov(RHSC->getAPInt(), Overflow);
if (Overflow) {
return getConstant(RHSC->getType(), 0, false);
}
return getUDivExpr(OtherDiv->getLHS(), getConstant(NewRHS));
}
}
// (A+B)/C --> (A/C + B/C) if safe and A/C and B/C can be folded.
if (const SCEVAddExpr *A = dyn_cast<SCEVAddExpr>(LHS)) {
SmallVector<const SCEV *, 4> Operands;

28
llvm/test/Analysis/ScalarEvolution/fold.ll
View File

@ -98,3 +98,31 @@ define void @test7(i32 %A) {
; CHECK-NEXT: --> 0
ret void
}
define i64 @test8(i64 %a) {
; CHECK-LABEL: @test8
%t0 = udiv i64 %a, 56
%t1 = udiv i64 %t0, 56
; CHECK: %t1
; CHECK-NEXT: --> (%a /u 3136)
ret i64 %t1
}
define i64 @test9(i64 %a) {
; CHECK-LABEL: @test9
%t0 = udiv i64 %a, 100000000000000
%t1 = udiv i64 %t0, 100000000000000
; CHECK: %t1
; CHECK-NEXT: --> 0
ret i64 %t1
}
define i64 @test10(i64 %a, i64 %b) {
; CHECK-LABEL: @test9
%t0 = udiv i64 %a, 100000000000000
%t1 = udiv i64 %t0, 100000000000000
%t2 = mul i64 %b, %t1
; CHECK: %t2
; CHECK-NEXT: --> 0
ret i64 %t2
}