[JumpThreading] Add test for llvm#79175 (NFC)

(cherry picked from commit 7143b45)

Author: nikic

llvm/test/Transforms/JumpThreading/pr79175.ll

@@ -0,0 +1,64 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S -passes=jump-threading < %s | FileCheck %s
+
+@f = external global i32
+
+; Make sure the value of @f is reloaded prior to the final comparison.
+; FIXME: This is a miscompile.
+define i32 @test(i64 %idx, i32 %val) {
+; CHECK-LABEL: define i32 @test(
+; CHECK-SAME: i64 [[IDX:%.*]], i32 [[VAL:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i64 [[IDX]], 1
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY:%.*]], label [[RETURN:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[F:%.*]] = load i32, ptr @f, align 4
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i32 [[F]], 0
+; CHECK-NEXT:    br i1 [[CMP1]], label [[COND_END_THREAD:%.*]], label [[COND_END:%.*]]
+; CHECK:       cond.end:
+; CHECK-NEXT:    [[CMP_I:%.*]] = icmp sgt i32 [[VAL]], 0
+; CHECK-NEXT:    [[COND_FR:%.*]] = freeze i1 [[CMP_I]]
+; CHECK-NEXT:    br i1 [[COND_FR]], label [[COND_END_THREAD]], label [[TMP0:%.*]]
+; CHECK:       cond.end.thread:
+; CHECK-NEXT:    [[F_RELOAD_PR:%.*]] = load i32, ptr @f, align 4
+; CHECK-NEXT:    br label [[TMP0]]
+; CHECK:       0:
+; CHECK-NEXT:    [[F_RELOAD:%.*]] = phi i32 [ [[F]], [[COND_END]] ], [ [[F_RELOAD_PR]], [[COND_END_THREAD]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = phi i32 [ 0, [[COND_END_THREAD]] ], [ [[VAL]], [[COND_END]] ]
+; CHECK-NEXT:    [[F_IDX:%.*]] = getelementptr inbounds i32, ptr @f, i64 [[IDX]]
+; CHECK-NEXT:    store i32 [[TMP1]], ptr [[F_IDX]], align 4
+; CHECK-NEXT:    [[CMP3:%.*]] = icmp slt i32 [[F_RELOAD]], 1
+; CHECK-NEXT:    br i1 [[CMP3]], label [[RETURN2:%.*]], label [[RETURN]]
+; CHECK:       return:
+; CHECK-NEXT:    ret i32 0
+; CHECK:       return2:
+; CHECK-NEXT:    ret i32 1
+;
+entry:
+  %cmp = icmp slt i64 %idx, 1
+  br i1 %cmp, label %for.body, label %return
+
+for.body:
+  %f = load i32, ptr @f, align 4
+  %cmp1 = icmp eq i32 %f, 0
+  br i1 %cmp1, label %cond.end, label %cond.false
+
+cond.false:
+  br label %cond.end
+
+cond.end:
+  %phi = phi i32 [ %val, %cond.false ], [ 1, %for.body ]
+  %cmp.i = icmp sgt i32 %phi, 0
+  %sel = select i1 %cmp.i, i32 0, i32 %phi
+  %f.idx = getelementptr inbounds i32, ptr @f, i64 %idx
+  store i32 %sel, ptr %f.idx, align 4
+  %f.reload = load i32, ptr @f, align 4
+  %cmp3 = icmp slt i32 %f.reload, 1
+  br i1 %cmp3, label %return2, label %return
+
+return:
+  ret i32 0
+
+return2:
+  ret i32 1
+}