[llvm] [InstCombine] Fold chained GEP with constant base into single GEP (PR #170439)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,83 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -passes=instcombine | FileCheck %s
+
+define ptr @src_origin(i32 %arg0, ptr %arg1) {
+; CHECK-LABEL: @src_origin(
+; CHECK-NEXT:    [[V1:%.*]] = icmp sgt i32 [[ARG0:%.*]], 3
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[V1]], i64 63252, i64 29452
+; CHECK-NEXT:    [[V3:%.*]] = getelementptr i8, ptr [[ARG1:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[V3]]
+;
+  %v0 = getelementptr i8, ptr %arg1, i64 8148
+  %v1 = icmp sgt i32 %arg0, 3
+  %v2 = select i1 %v1, i64 55104, i64 21304
+  %v3 = getelementptr i8, ptr %v0, i64 %v2
+  ret ptr %v3
+}
+
+define ptr @src_nuw(i32 %arg0, ptr %arg1) {
+; CHECK-LABEL: @src_nuw(
+; CHECK-NEXT:    [[V1:%.*]] = icmp sgt i32 [[ARG0:%.*]], 3
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[V1]], i64 63252, i64 29452
+; CHECK-NEXT:    [[V3:%.*]] = getelementptr nuw i8, ptr [[ARG1:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[V3]]
+;
+  %v0 = getelementptr nuw i8, ptr %arg1, i64 8148
+  %v1 = icmp sgt i32 %arg0, 3
+  %v2 = select i1 %v1, i64 55104, i64 21304
+  %v3 = getelementptr nuw i8, ptr %v0, i64 %v2
+  ret ptr %v3
+}
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nikic wrote:

Please also test the intersection behavior. E.g. that `inbounds nuw` + `nuw` only gives `nuw`.

https://github.com/llvm/llvm-project/pull/170439