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[InstCombine] Intersect nowrap flags between geps while folding into phi #115901

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Merged
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Nov 13, 2024
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[InstCombine] Intersect nowrap flags between geps while folding into phi #115901

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0f44d72
[InstCombine] Precommit test for PR115901 (NFC)
antoniofrighetto Nov 12, 2024
929cbe7
[InstCombine] Intersect nowrap flags between geps while folding into phi
antoniofrighetto Nov 12, 2024
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3 changes: 2 additions & 1 deletion llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
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Expand Up @@ -545,7 +545,8 @@ Instruction *InstCombinerImpl::foldPHIArgGEPIntoPHI(PHINode &PN) {
// especially bad when the PHIs are in the header of a loop.
bool NeededPhi = false;

GEPNoWrapFlags NW = GEPNoWrapFlags::all();
// Remember flags of the first phi-operand getelementptr.
GEPNoWrapFlags NW = FirstInst->getNoWrapFlags();

// Scan to see if all operands are the same opcode, and all have one user.
for (Value *V : drop_begin(PN.incoming_values())) {
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2 changes: 1 addition & 1 deletion llvm/test/Transforms/InstCombine/opaque-ptr.ll
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Expand Up @@ -549,7 +549,7 @@ define ptr @phi_of_gep_flags_1(i1 %c, ptr %p) {
; CHECK: else:
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
; CHECK-NEXT: [[PHI:%.*]] = getelementptr nusw nuw i8, ptr [[P:%.*]], i64 4
; CHECK-NEXT: [[PHI:%.*]] = getelementptr nusw i8, ptr [[P:%.*]], i64 4
; CHECK-NEXT: ret ptr [[PHI]]
;
br i1 %c, label %if, label %else
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28 changes: 28 additions & 0 deletions llvm/test/Transforms/InstCombine/phi.ll
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Expand Up @@ -2794,3 +2794,31 @@ BB4: ; preds = %BB3, %BB2, %BB1, %BB
BB5: ; preds = %BB4
ret void
}

define i64 @wrong_gep_arg_into_phi(ptr noundef %ptr) {
; CHECK-LABEL: @wrong_gep_arg_into_phi(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[FOR_COND:%.*]]
; CHECK: for.cond:
; CHECK-NEXT: [[PTR_PN:%.*]] = phi ptr [ [[PTR:%.*]], [[ENTRY:%.*]] ], [ [[DOTPN:%.*]], [[FOR_COND]] ]
; CHECK-NEXT: [[DOTPN]] = getelementptr i8, ptr [[PTR_PN]], i64 1
; CHECK-NEXT: [[VAL:%.*]] = load i8, ptr [[DOTPN]], align 1
; CHECK-NEXT: [[COND_NOT:%.*]] = icmp eq i8 [[VAL]], 0
; CHECK-NEXT: br i1 [[COND_NOT]], label [[EXIT:%.*]], label [[FOR_COND]]
; CHECK: exit:
; CHECK-NEXT: ret i64 0
;
entry:
%add.ptr = getelementptr i8, ptr %ptr, i64 1
br label %for.cond

for.cond: ; preds = %for.cond, %entry
%.pn = phi ptr [ %add.ptr, %entry ], [ %incdec.ptr, %for.cond ]
%val = load i8, ptr %.pn, align 1
%cond = icmp ne i8 %val, 0
%incdec.ptr = getelementptr inbounds nuw i8, ptr %.pn, i64 1
br i1 %cond, label %for.cond, label %exit

exit: ; preds = %for.cond
ret i64 0
}
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