[libc-commits] [libc] [libc][stdfix] Guard DiviFxTest shift edge cases against narrow IntType (PR #209970)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: sohail (sohail103)

<details>
<summary>Changes</summary>

`1 << INTEGRAL_LEN`/`1 << FRACTION_LEN` assumed IntType always has enough bits which is false for long int / long accum on ILP32 targets. This PR adds guards to skip those checks when they don't fit.

Fixes riscv32 buildbot failure from #<!-- -->206115.

---
Full diff: https://github.com/llvm/llvm-project/pull/209970.diff


1 Files Affected:

- (modified) libc/test/src/stdfix/DiviFxTest.h (+4-2) 


``````````diff
diff --git a/libc/test/src/stdfix/DiviFxTest.h b/libc/test/src/stdfix/DiviFxTest.h
index 06c4868367858..6bbfcd0f8e9fd 100644
--- a/libc/test/src/stdfix/DiviFxTest.h
+++ b/libc/test/src/stdfix/DiviFxTest.h
@@ -108,7 +108,8 @@ class DiviFxTest : public LIBC_NAMESPACE::testing::Test {
 
     // Only valid when integral bits (excluding sign) exceed fraction bits.
     // Otherwise 1<<FRACTION_LEN may not fit in IntType.
-    if constexpr ((FXRep::INTEGRAL_LEN) > FXRep::FRACTION_LEN) {
+    if constexpr ((FXRep::INTEGRAL_LEN) > FXRep::FRACTION_LEN &&
+                  FXRep::FRACTION_LEN < cpp::numeric_limits<IntType>::digits) {
       constexpr IntType epsilon_result = static_cast<IntType>(1)
                                          << FXRep::FRACTION_LEN;
       EXPECT_EQ(func(1, epsilon), epsilon_result);
@@ -119,7 +120,8 @@ class DiviFxTest : public LIBC_NAMESPACE::testing::Test {
       }
     }
 
-    if constexpr (has_integral) {
+    if constexpr (has_integral &&
+                  FXRep::INTEGRAL_LEN < cpp::numeric_limits<IntType>::digits) {
       constexpr IntType largest_positive =
           ((static_cast<IntType>(1) << FXRep::INTEGRAL_LEN) - 1);
       EXPECT_EQ(func(largest_positive, static_cast<FXType>(largest_positive)),

``````````

</details>


https://github.com/llvm/llvm-project/pull/209970