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[Bitcode] Fix constexpr expansion creating invalid PHIs #141560

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Merged
merged 1 commit into from
May 27, 2025
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[Bitcode] Fix constexpr expansion creating invalid PHIs #141560

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8 changes: 6 additions & 2 deletions llvm/lib/Bitcode/Reader/BitcodeReader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6095,14 +6095,18 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
// seen value here, to avoid expanding a constant expression multiple
// times.
auto It = Args.find(BB);
BasicBlock *EdgeBB = ConstExprEdgeBBs.lookup({BB, CurBB});
if (It != Args.end()) {
PN->addIncoming(It->second, BB);
// If this predecessor was also replaced with a constexpr basic
// block, it must be de-duplicated.
if (!EdgeBB) {
PN->addIncoming(It->second, BB);
}
continue;
}

// If there already is a block for this edge (from a different phi),
// use it.
BasicBlock *EdgeBB = ConstExprEdgeBBs.lookup({BB, CurBB});
if (!EdgeBB) {
// Otherwise, use a temporary block (that we will discard if it
// turns out to be unnecessary).
Expand Down
30 changes: 30 additions & 0 deletions llvm/test/Bitcode/constexpr-to-instr-dups.ll
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@@ -0,0 +1,30 @@
; RUN: opt -expand-constant-exprs %s.bc -S | FileCheck %s
@foo = external constant i32

define i32 @test(i32 %arg) {
entry:
switch i32 %arg, label %cont [
i32 1, label %cont
i32 2, label %nonconst
]

nonconst:
%cmp = icmp ne i32 %arg, 2
br i1 %cmp, label %cont, label %cont

; CHECK-LABEL: phi.constexpr:
; CHECK-NEXT: %constexpr = ptrtoint ptr @foo to i32
; CHECK-NEXT: %constexpr1 = or i32 %constexpr, 5
; CHECK-NEXT: br label %cont


; CHECK-LABEL: cont:
; CHECK-NEXT: %res = phi i32 [ %constexpr1, %phi.constexpr ], [ 1, %nonconst ], [ 1, %nonconst ]
; CHECK-NEXT: ret i32 %res
cont:
%res = phi i32 [or (i32 5, i32 ptrtoint (ptr @foo to i32)), %entry],
[or (i32 5, i32 ptrtoint (ptr @foo to i32)), %entry],
[1, %nonconst],
[1, %nonconst]
ret i32 %res
}
Binary file added llvm/test/Bitcode/constexpr-to-instr-dups.ll.bc
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4 changes: 2 additions & 2 deletions llvm/test/Bitcode/constexpr-to-instr.ll
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@@ -1,4 +1,4 @@
; RUN: llvm-dis -expand-constant-exprs < %s.bc | FileCheck %s
; RUN: opt -expand-constant-exprs -S %s.bc | FileCheck %s

@g = extern_weak global i32
@g2 = extern_weak global i32
Expand Down Expand Up @@ -225,7 +225,7 @@ define i64 @test_phi_multiple_identical_predecessors(i32 %x) {
; CHECK-NEXT: %constexpr = ptrtoint ptr @g to i64
; CHECK-NEXT: br label %join
; CHECK: join:
; CHECK-NEXT: %phi = phi i64 [ %constexpr, %phi.constexpr ], [ %constexpr, %phi.constexpr ], [ 0, %default ]
; CHECK-NEXT: %phi = phi i64 [ %constexpr, %phi.constexpr ], [ 0, %default ]
; CHECK-NEXT: ret i64 %phi
entry:
switch i32 %x, label %default [
Expand Down