Extended Description

To reproduce:

clang -cc1 -triple i386-pc-win32 -mstackrealign -target-cpu pentium4 -fms-extensions -S -o - b.ii

We're miscompiling this statement:

updateAnimations(SMILTime(m_presetStartTime), m_presetStartTime ? true : false);

In Clang's asm printout, we have this:

    movsd   32(%edx), %xmm0
    xorps   %xmm1, %xmm1
    cmpneqsd        %xmm0, %xmm1
    movd    %xmm1, %rsi

Note that the last instruction tries to move xmm1 to a 64-bit register, but we're targeting i386.

Disassembling the object file shows different instructions:

000000AE: F2 0F 10 42 20 movsd xmm0,mmword ptr [edx+20h]
000000B3: 0F 57 C9 xorps xmm1,xmm1
000000B6: F2 0F C2 C8 04 cmpneqsd xmm1,xmm0
000000BB: 66 0F 7E CE movd esi,xmm1

Turns out our 64-bit move to rsi becomes a 32-bit move into esi? But esi is used as base pointer in this function; we have now clobbered it and will crash a few lines down.

The 64-bit move looks like this (this is from "Before Expand ISel Pseudo-instructions"):

%vreg32<def> = FsFLD0SD; FR64:%vreg32
%vreg33<def,tied1> = CMPSDrr %vreg32<tied0>, %vreg31<kill>, 4; FR64:%vreg33,%vreg32,%vreg31
%vreg34<def> = MOVSDto64rr %vreg33<kill>; GR64:%vreg34 FR64:%vreg33

after register allocation, we think we're moving into rsi:

%XMM1<def> = FsFLD0SD
%XMM1<def,tied1> = CMPSDrr %XMM1<tied0>, %XMM0<kill>, 4
%RSI<def> = MOVSDto64rr %XMM1<kill>

There's something strange going on here :)

(This is reduced from WebCore::SMILTimeContainer::begin.)