Fix floating-point FMA to integer negation pattern to prevent ICEs
Correct a constraint in a negation pattern to prevent floating-point FMAs from being incorrectly folded into integer operations.
This commit fixes a bug in a GCC optimization pattern that incorrectly allowed floating-point Fused Multiply-Add (FMA) operations to be folded into integer negation patterns. The erroneous constraint allowed the pattern to match even when the operands were floating-point types, leading to incorrect type conversions and an internal compiler error (ICE) due to mismatched SVE attributes. The fix adjusts the pattern’s guard to ensure it only applies to integral types, thereby preventing these incorrect transformations and compiler crashes.
In Details
The optimization introduced in GCC commit gca2920882be (referenced internally) contained a flaw in match.pd that mistakenly allowed floating-point FMAs to be matched by a pattern intended for integer operations. Specifically, pattern match.pd:10328 was applied to SVE vector types (svfloat32_t) when the input operands were unsigned integers, leading to an ICE because the SVE vector attributes on the result did not align with the expected integer output. This change modifies the constraint in match.pd to restrict this pattern to integral types only, ensuring that floating-point FMAs a…
- FMA (Fused Multiply-Add)
- A floating-point operation that performs a multiplication and an addition in a single step, often with higher precision and performance than separate multiply and add operations.
- ICE (Internal Compiler Error)
- An error that occurs within the compiler itself, indicating a bug or an unexpected state during the compilation process. These typically halt compilation.
- SVE (Scalable Vector Extension)
- An advanced vector processing instruction set for ARM processors, allowing operations on vectors whose length can vary dynamically.
- Integral Types
- Data types that represent whole numbers, such as integers (int, long, etc.), as opposed to floating-point types (float, double).
- Pattern Matching
- A technique used by compilers to identify specific code structures (patterns) in the intermediate representation (IR) that can be transformed or optimized.