[all-commits] [llvm/llvm-project] f162be: [RISCV] Use unsigned comparison for stack clash pr...

[Nick Desaulniers via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f162be248636046a20e71209e139347e084b637a
      https://github.com/llvm/llvm-project/commit/f162be248636046a20e71209e139347e084b637a
  Author: Nick Desaulniers <ndesaulniers at google.com>
  Date:   2026-04-16 (Thu, 16 Apr 2026)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/test/CodeGen/RISCV/rvv/stack-probing-dynamic.ll
    M llvm/test/CodeGen/RISCV/stack-clash-prologue.ll

  Log Message:
  -----------
  [RISCV] Use unsigned comparison for stack clash probing loop (#192485)

The stack clash probing loop generated in `emitDynamicProbedAlloc` used
a signed comparison (`RISCV::COND_BLT`) to determine when the allocation
target had been reached.

In 32-bit mode, memory addresses above `0x80000000` have the sign bit
set. If the stack pointer lands in this region, treating the addresses
as signed integers causes the comparison logic to fail.

This patch changes the condition code to `RISCV::COND_BLTU` (Branch if
Less Than Unsigned), which generates an unsigned comparison. This
ensures that addresses are treated correctly as unsigned quantities on
all targets.

On 64-bit systems, this change has no practical effect on valid
user-space addresses because they do not use the sign bit (being
restricted to the lower half of the address space). However, using
unsigned comparison is the correct behavior for pointer arithmetic and
bounds checks.

Link: #192355



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