On Fri, Aug 14, 2026 at 2:21 PM Richard Biener <[email protected]> wrote: > > On Thu, Aug 13, 2026 at 10:32 AM H.J. Lu <[email protected]> wrote: > > > > On Thu, Aug 13, 2026 at 3:59 PM Richard Biener > > <[email protected]> wrote: > > > > > > On Wed, Aug 12, 2026 at 4:25 PM H.J. Lu <[email protected]> wrote: > > > > > > > > Double unaligned load and store cost if the vector mode size is less > > > > than 8 bytes and the number of vector element is less than 4 when SSE > > > > is enabled to avoid using vector instructions on unaligned short data > > > > with 2 vector elements so that for > > > > > > > > extern char *var1; > > > > extern int var2; > > > > > > > > void > > > > func (void) > > > > { > > > > var2 = var1[1] + var1[0]; > > > > } > > > > > > > > we generate > > > > > > > > movq var1(%rip), %rdx > > > > movsbl 1(%rdx), %eax > > > > movsbl (%rdx), %edx > > > > addl %edx, %eax > > > > movl %eax, var2(%rip) > > > > > > > > instead of > > > > > > > > movq var1(%rip), %rax > > > > pxor %xmm1, %xmm1 > > > > pinsrw $0, (%rax), %xmm0 > > > > pcmpgtb %xmm0, %xmm1 > > > > punpcklbw %xmm1, %xmm0 > > > > movdqa %xmm0, %xmm1 > > > > psraw $15, %xmm1 > > > > punpcklwd %xmm1, %xmm0 > > > > movd %xmm0, %edx > > > > pshufd $0xe5, %xmm0, %xmm2 > > > > movd %xmm2, %eax > > > > addl %edx, %eax > > > > movl %eax, var2(%rip) > > > > > > > > with -O2 -march=x86-64. > > > > > > > > Compile PR 125100 tests with -mno-sse since unaligned V2QImode load is > > > > no > > > > longer generated when SSE is enabled. > > > > > > Instead of just doubling the load/store cost can we try to more accurately > > > model the cost of loading of 1, 2 or 4 byte vectors to SSE registers? > > > For example with SSE4 we get > > > > > > movq var1(%rip), %rax > > > pinsrw $0, (%rax), %xmm0 > > > pmovsxbd %xmm0, %xmm0 > > > movd %xmm0, %edx > > > pextrd $1, %xmm0, %eax > > > addl %edx, %eax > > > movl %eax, var2(%rip) > > > ret > > > > Is this really better than > > > > movq var1(%rip), %rdx > > movswl 2(%rdx), %eax > > movswl (%rdx), %edx > > addl %edx, %eax > > movl %eax, var2(%rip) > > No, but it's better than the SSE2 version ;) If you just want to prevent > these small vectorizations you can deny any scalar_cost < 30 vectorizations > or so. I thought the point is to make the costing more precise - you > correctly identified at least HImode -> XMM loads/stores to be not accurately > costed. >
The problems are V2QImode and V2HImode. Others seem OK. -- H.J.
