[llvm-bugs] [Bug 46662] New: merge truncated stores

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=46662

            Bug ID: 46662
           Summary: merge truncated stores
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: spatel+llvm at rotateright.com
                CC: llvm-bugs at lists.llvm.org

void i32(long long x, int* p) {
  int a = x;
  int b = x >> 32;
  p[0] = a;
  p[1] = b;
}

define void @i32(i64 %0, i32* nocapture %1) {
  %3 = trunc i64 %0 to i32
  %4 = lshr i64 %0, 32
  %5 = trunc i64 %4 to i32
  store i32 %3, i32* %1, align 4
  %6 = getelementptr inbounds i32, i32* %1, i64 1
  store i32 %5, i32* %6, align 4
  ret void
}

--------------------------------------------------------------------------

Compiles to x86-64:
  movl %edi, (%rsi)
  shrq $32, %rdi
  movl %edi, 4(%rsi)
  retq

--------------------------------------------------------------------------

But that could be only:
  movq %rdi, (%rsi)

In DAGCombiner, we have MatchStoreCombine(), but it only handles 8-bit; we have
mergeConsecutiveStores(), but it doesn't look at trunc patterns.

https://godbolt.org/z/xMPxT9

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20200709/1eb280ce/attachment.html>