[llvm-bugs] [Bug 37939] New: Missed pattern B+(-C)*A

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=37939

            Bug ID: 37939
           Summary: Missed pattern B+(-C)*A
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

Code:
int foo2(int x, int y)  {
      return x + -2 *y;
}

int foo3(int x, int y)  {
      return x + -3 *y;
}

int foo4(int x, int y)  {
      return x + -4 *y;
}

Clang trunk:
foo2(int, int): # @foo2(int, int)
  add esi, esi
  sub edi, esi
  mov eax, edi
  ret
foo3(int, int): # @foo3(int, int)
  lea eax, [rsi + 2*rsi]
  neg eax
  add eax, edi
  ret
foo4(int, int): # @foo4(int, int)
  shl esi, 2
  sub edi, esi
  mov eax, edi
  ret

GCC 8:
foo2(int, int):
  neg esi
  lea eax, [rdi+rsi*2]
  ret
foo3(int, int):
  lea eax, [0+rsi*4]
  sub esi, eax
  lea eax, [rsi+rdi]
  ret
foo4(int, int):
  neg esi
  lea eax, [rdi+rsi*4]
  ret

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