[clang] [llvm] [InstCombine] Canonicalize constant GEPs to i8 source element type (PR #68882)

[Nikita Popov via cfe-commits]

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@@ -560,14 +560,15 @@ define i32 @test28() nounwind  {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[ORIENTATIONS:%.*]] = alloca [1 x [1 x %struct.x]], align 8
 ; CHECK-NEXT:    [[T3:%.*]] = call i32 @puts(ptr noundef nonnull dereferenceable(1) @.str) #[[ATTR0]]
+; CHECK-NEXT:    [[T45:%.*]] = getelementptr inbounds i8, ptr [[ORIENTATIONS]], i64 1
 ; CHECK-NEXT:    br label [[BB10:%.*]]
 ; CHECK:       bb10:
 ; CHECK-NEXT:    [[INDVAR:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[INDVAR_NEXT:%.*]], [[BB10]] ]
 ; CHECK-NEXT:    [[T12_REC:%.*]] = xor i32 [[INDVAR]], -1
 ; CHECK-NEXT:    [[TMP0:%.*]] = sext i32 [[T12_REC]] to i64
-; CHECK-NEXT:    [[T12:%.*]] = getelementptr inbounds [1 x [1 x %struct.x]], ptr [[ORIENTATIONS]], i64 1, i64 0, i64 [[TMP0]]
+; CHECK-NEXT:    [[T12:%.*]] = getelementptr inbounds [[STRUCT_X:%.*]], ptr [[T45]], i64 [[TMP0]]
 ; CHECK-NEXT:    [[T16:%.*]] = call i32 (ptr, ...) @printf(ptr noundef nonnull dereferenceable(1) @.str1, ptr nonnull [[T12]]) #[[ATTR0]]
-; CHECK-NEXT:    [[T84:%.*]] = icmp eq i32 [[INDVAR]], 0
+; CHECK-NEXT:    [[T84:%.*]] = icmp eq ptr [[T12]], [[ORIENTATIONS]]
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nikic wrote:

Turns out this one is not the indexed compare fold, but the `icmp %p, gep(%p)` fold. Now we have two GEPs though and it no longer triggers.

https://github.com/llvm/llvm-project/pull/68882