[llvm] [InstCombine] Fold icmp(constants[x]) when the range of x is given (PR #67093)

[Nikita Popov via llvm-commits]

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@@ -334,3 +327,143 @@ define i1 @test10_struct_arr_noinbounds_i64(i64 %x) {
   %r = icmp eq i32 %q, 9
   ret i1 %r
 }
+
+
+ at CG = constant [4 x i32] [i32 1, i32 2, i32 3, i32 4]
+
+; TODO: Fold it globally.
+define i1 @cmp_load_constant_array0(i64 %x){
+; CHECK-LABEL: @cmp_load_constant_array0(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[COND:%.*]] = icmp ult i64 [[X:%.*]], 2
+; CHECK-NEXT:    br i1 [[COND]], label [[CASE1:%.*]], label [[CASE2:%.*]]
+; CHECK:       case2:
+; CHECK-NEXT:    ret i1 false
+; CHECK:       case1:
+; CHECK-NEXT:    ret i1 true
+;
+entry:
+  %cond = icmp ult i64 %x, 2
+  br i1 %cond, label %case1, label %case2
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nikic wrote:

I think it would be better to omit this condition from the test, so we can see the direct result of the transform, without additional implication reasoning. Same for the next test.

https://github.com/llvm/llvm-project/pull/67093