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[IndVarSimplify] Forget phi value after changing incoming value. 

This fixes an issue exposed by D71539, where IndVarSimplify tries
to access an invalid cached SCEV expression after making changes to the
underlying PHI instruction earlier.

When changing the incoming value of a PHI, forget the cached SCEV for
the PHI.
This commit is contained in:
Florian Hahn 2021-09-29 14:38:35 +01:00
parent 92ea624a13
commit 0b4a4cc72d
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GPG Key ID: 61D7554B5CECDC0D
2 changed files with 45 additions and 0 deletions
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1
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -494,6 +494,7 @@ bool IndVarSimplify::rewriteFirstIterationLoopExitValues(Loop *L) {
MadeAnyChanges = true;
PN.setIncomingValue(IncomingValIdx,
ExitVal->getIncomingValue(PreheaderIdx));
SE->forgetValue(&PN);
}
}
}

44
llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll Normal file
View File

@ -0,0 +1,44 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -passes='loop(indvars,loop-deletion)' -S %s | FileCheck %s
; Make sure indvarsimplify properly forgets the exit value %p.2.lcssa phi after
; modifying it. Loop deletion is required to show the incorrect use of the cached
; SCEV value.
define void @test(i1 %c) {
; CHECK-LABEL: @test(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[HEADER_1:%.*]]
; CHECK: header.1.loopexit:
; CHECK-NEXT: br label [[HEADER_1_BACKEDGE:%.*]]
; CHECK: header.1:
; CHECK-NEXT: br label [[HEADER_2:%.*]]
; CHECK: header.2:
; CHECK-NEXT: br i1 [[C:%.*]], label [[LATCH_1:%.*]], label [[LATCH_2:%.*]]
; CHECK: latch.1:
; CHECK-NEXT: br label [[HEADER_1_LOOPEXIT:%.*]]
; CHECK: latch.2:
; CHECK-NEXT: br label [[HEADER_1_BACKEDGE]]
; CHECK: header.1.backedge:
; CHECK-NEXT: br label [[HEADER_1]]
;
entry:
br label %header.1
header.1:
%p.1 = phi i32 [ 0, %entry ], [ %p.2.lcssa, %latch.2 ], [ 0, %latch.1 ]
br label %header.2
header.2:
%p.2 = phi i32 [ %p.1, %header.1 ], [ %p.2.next, %latch.1 ]
br i1 %c, label %latch.1, label %latch.2
latch.1:
%p.2.next = add i32 %p.2, 1
br i1 false, label %header.2, label %header.1
latch.2:
%p.2.lcssa = phi i32 [ %p.2, %header.2 ]
br label %header.1
}