[clang] [clang][CodeGen][UBSan] Fixing shift-exponent generation for _BitInt (PR #80515)

[Björn Pettersson via cfe-commits]

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@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 %s -O0 -fsanitize=shift-exponent -emit-llvm -o - | FileCheck %s
+
+// Checking that the code generation is using the unextended/untruncated
+// exponent values and capping the values accordingly
+
+// CHECK-LABEL: define{{.*}} i32 @test_left_variable
+int test_left_variable(unsigned _BitInt(5) b, unsigned _BitInt(2) e) {
+  // CHECK: [[E_REG:%.+]] = load [[E_SIZE:i2]]
+  // CHECK: icmp ule [[E_SIZE]] [[E_REG]], -1
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bjope wrote:

So this test case show something that we perhaps should follow up an optimize later.
Not sure if the idea is to make the frontend simple at let the middle end optimize it away, but it is a bit stupid to emit the check here when comparing with -1.

https://github.com/llvm/llvm-project/pull/80515