[llvm-branch-commits] X86: Add X86TargetLowering::isProfitableToHoist hook for immediate operands. (PR #141326)

[Peter Collingbourne via llvm-branch-commits]

pcc wrote:

I'm fixing the code generation for the test cases that I'm adding (inhibit-zext-constant-hoist.ll) which were all extracted from a build of a large internal program built with CFI. Previously f1 looked like this where align was hoisted:
```
f1:                                     # @f1
	.cfi_startproc
# %bb.0:
	movl	$__typeid__ZTS1S_align, %eax
	movzbl	%al, %ecx
	movb	$64, %al
	subb	%cl, %al
	movzbl	%al, %eax
	testl	%edi, %edi
	je	.LBB0_3
# %bb.1:
	movq	(%rsi), %r8
	movl	$__typeid__ZTS1S_global_addr, %edx
	movq	%r8, %rdi
	subq	%rdx, %rdi
	movq	%rdi, %rdx
                                        # kill: def $cl killed $cl killed $rcx
	shrq	%cl, %rdx
	movl	%eax, %ecx
	shlq	%cl, %rdi
	orq	%rdx, %rdi
	cmpq	$__typeid__ZTS1S_size_m1 at ABS8, %rdi
	jbe	.LBB0_4
.LBB0_2:
	ud1l	2(%eax), %eax
.LBB0_3:
	movq	(%rdx), %r8
	movl	$__typeid__ZTS1S_global_addr, %esi
	movq	%r8, %rdi
	subq	%rsi, %rdi
	movq	%rdi, %rsi
                                        # kill: def $cl killed $cl killed $rcx
	shrq	%cl, %rsi
	movl	%eax, %ecx
	shlq	%cl, %rdi
	orq	%rsi, %rdi
	cmpq	$__typeid__ZTS1S_size_m1 at ABS8, %rdi
	movq	%rdx, %rsi
	ja	.LBB0_2
.LBB0_4:
	movq	%rsi, %rdi
	jmpq	*(%r8)                          # TAILCALL
.Lfunc_end0:
	.size	f1, .Lfunc_end0-f1
	.cfi_endproc
```
Now f1 looks like this:
```
f1:                                     # @f1
	.cfi_startproc
# %bb.0:
	testl	%edi, %edi
	je	.LBB0_3
# %bb.1:
	movq	(%rsi), %rax
	movl	$__typeid__ZTS1S_global_addr, %ecx
	movq	%rax, %rdx
	subq	%rcx, %rdx
	rorq	$__typeid__ZTS1S_align, %rdx
	cmpq	$__typeid__ZTS1S_size_m1 at ABS8, %rdx
	jbe	.LBB0_4
.LBB0_2:
	ud1l	2(%eax), %eax
.LBB0_3:
	movq	(%rdx), %rax
	movl	$__typeid__ZTS1S_global_addr, %ecx
	movq	%rax, %rsi
	subq	%rcx, %rsi
	rorq	$__typeid__ZTS1S_align, %rsi
	cmpq	$__typeid__ZTS1S_size_m1 at ABS8, %rsi
	movq	%rdx, %rsi
	ja	.LBB0_2
.LBB0_4:
	movq	%rsi, %rdi
	jmpq	*(%rax)                         # TAILCALL
.Lfunc_end0:
	.size	f1, .Lfunc_end0-f1
	.cfi_endproc
```
The other cases look similar before my change.

The poor codegen issue was introduced (I believe) by https://github.com/llvm/llvm-project/pull/71040 which removed the zext ConstantExprs that LowerTypeTests was using to keep everything in the same basic block for matching.

I think that because it's the zext being hoisted and not the shifts it wouldn't make a difference to use fshl/fshr but I can check.

https://github.com/llvm/llvm-project/pull/141326