[llvm] [Attributor] Change allocation size and load/store offsets using AAPointerInfo for Alloca instructions and keep track of instructions causing an Access (PR #72029)

[Vidush Singhal via llvm-commits]

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@@ -10,11 +10,11 @@ define void @foo(ptr %ptr) {
 ; TUNIT-LABEL: define {{[^@]+}}@foo
 ; TUNIT-SAME: (ptr nofree readnone captures(none) [[PTR:%.*]]) #[[ATTR0:[0-9]+]] {
 ; TUNIT-NEXT:  entry:
-; TUNIT-NEXT:    [[TMP0:%.*]] = alloca [[STRUCT_TEST_A:%.*]], align 8
+; TUNIT-NEXT:    [[TMP0:%.*]] = alloca [8 x i8], align 1
 ; TUNIT-NEXT:    br label [[CALL_BR:%.*]]
 ; TUNIT:       call.br:
-; TUNIT-NEXT:    [[TMP1:%.*]] = getelementptr inbounds [[STRUCT_TEST_A]], ptr [[TMP0]], i64 0, i32 2
-; TUNIT-NEXT:    tail call void @bar(ptr noalias nofree noundef nonnull readonly byval([[STRUCT_TEST_A]]) align 8 captures(none) dereferenceable(24) [[TMP0]]) #[[ATTR2:[0-9]+]]
+; TUNIT-NEXT:    [[NEWGEP:%.*]] = getelementptr [8 x i8], ptr [[TMP0]], i64 0
+; TUNIT-NEXT:    tail call void @bar(ptr noalias nofree noundef nonnull readonly byval([[STRUCT_TEST_A:%.*]]) align 8 captures(none) dereferenceable(24) [[TMP0]]) #[[ATTR2:[0-9]+]]
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vidsinghal wrote:

Would it be fine to use the same alignment as the old Alloca Instruction for the first case for the new Alloca?

The best way to solve this seems to be to ensure that for all uses of the Alloca, if there is a cast instruction, then  need to change the type of the cast.

https://github.com/llvm/llvm-project/pull/72029