[LLVMdev] Weird volatile propagation ?

[Arnaud A. de Grandmaison]

Hi All,

Using clang+llvm at head, I noticed a weird behaviour with the following
reduced testcase :

$ cat test.c 

#include <stdint.h>

struct R {
  uint16_t a;
  uint16_t b;
};

volatile struct R * const addr = (volatile struct R *) 416;

void test(uint16_t a)
{
  struct R r = { a, 1 };
  *addr = r;
}

$ clang -O2 -o - -emit-llvm -S -c test.c 
; ModuleID = 'test.c'
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

%struct.R = type { i16, i16 }

@addr = constant %struct.R* inttoptr (i64 416 to %struct.R*), align 8

define void @test(i16 zeroext %a) nounwind uwtable {
  %r.sroa.0 = alloca i16, align 2
  %r.sroa.1 = alloca i16, align 2
  store i16 %a, i16* %r.sroa.0, align 2
  store i16 1, i16* %r.sroa.1, align 2
  %r.sroa.0.0.load3 = load volatile i16* %r.sroa.0, align 2
  store volatile i16 %r.sroa.0.0.load3, i16* inttoptr (i64 416 to i16*), align 32
  %r.sroa.1.0.load2 = load volatile i16* %r.sroa.1, align 2
  store volatile i16 %r.sroa.1.0.load2, i16* inttoptr (i64 418 to i16*), align 2
  ret void
}


When I would have expected something like :

define void @test(i16 zeroext %a) nounwind uwtable {
  store volatile i16 %a, i16* inttoptr (i64 416 to i16*), align 2
  store volatile i16 1, i16* inttoptr (i64 418 to i16*), align 2
  ret void
}

Using LLVM-3.1, I get the expected code. Would this ring a bell to anybody ?

Cheers,

-- 
Arnaud de Grandmaison