Shrinking arithmetic in LLVM

shrink.ll

define i128 @test_shrink_add_1(i128 %a, i128 %b) {
  %small_a = trunc i128 %a to i64
  %small_b = trunc i128 %b to i64
  %big_a = zext i64 %small_a to i128
  %big_b = zext i64 %small_b to i128

  %r = add i128 %big_a, %big_b
  ret i128 %r
}

define i128 @test_shrink_add_2(i128 %a, i128 %b) {
  %small_a = trunc i128 %a to i64
  %small_b = trunc i128 %b to i64
  %big_a = zext i64 %small_a to i128
  %big_b = zext i64 %small_b to i128

  %r = add i128 %big_a, %big_b
  %small_r = trunc i128 %r to i64
  %big_r = zext i64 %small_r to i128
  ret i128 %big_r
}

define i128 @test_shrink_mul_1(i128 %a, i128 %b) {
  %small_a = trunc i128 %a to i64
  %small_b = trunc i128 %b to i64
  %big_a = zext i64 %small_a to i128
  %big_b = zext i64 %small_b to i128

  %r = mul i128 %big_a, %big_b
  ret i128 %r
}

define i128 @test_shrink_mul_2(i128 %a, i128 %b) {
  %small_a = trunc i128 %a to i64
  %small_b = trunc i128 %b to i64
  %big_a = zext i64 %small_a to i128
  %big_b = zext i64 %small_b to i128

  %r = mul i128 %big_a, %big_b
  %small_r = trunc i128 %r to i64
  %big_r = zext i64 %small_r to i128
  ret i128 %big_r
}

shrink.opt.ll

; opt shrink.ll -S -O3 > shrink.opt.ll

; Function Attrs: norecurse nounwind readnone
define i128 @test_shrink_add_1(i128 %a, i128 %b) #0 {
  %big_a = and i128 %a, 18446744073709551615
  %big_b = and i128 %b, 18446744073709551615
  %r = add nuw nsw i128 %big_b, %big_a
  ret i128 %r
}

; Function Attrs: norecurse nounwind readnone
define i128 @test_shrink_add_2(i128 %a, i128 %b) #0 {
  %r = add i128 %b, %a
  %big_r = and i128 %r, 18446744073709551615
  ret i128 %big_r
}

; Function Attrs: norecurse nounwind readnone
define i128 @test_shrink_mul_1(i128 %a, i128 %b) #0 {
  %big_a = and i128 %a, 18446744073709551615
  %big_b = and i128 %b, 18446744073709551615
  %r = mul nuw i128 %big_b, %big_a
  ret i128 %r
}

; Function Attrs: norecurse nounwind readnone
define i128 @test_shrink_mul_2(i128 %a, i128 %b) #0 {
  %big_a = and i128 %a, 18446744073709551615
  %big_b = and i128 %b, 18446744073709551615
  %r = mul nuw i128 %big_b, %big_a
  %big_r = and i128 %r, 18446744073709551615
  ret i128 %big_r
}

attributes #0 = { norecurse nounwind readnone }

shrink.opt.s

# llc -O3 shrink.opt.ll

	.text
	.file	"shrink.opt.ll"
	.globl	test_shrink_add_1
	.align	16, 0x90
	.type	test_shrink_add_1,@function
test_shrink_add_1:                      # @test_shrink_add_1
# BB#0:
	addq	%rdx, %rdi
	sbbq	%rdx, %rdx
	andl	$1, %edx
	movq	%rdi, %rax
	retq
.Lfunc_end0:
	.size	test_shrink_add_1, .Lfunc_end0-test_shrink_add_1

	.globl	test_shrink_add_2
	.align	16, 0x90
	.type	test_shrink_add_2,@function
test_shrink_add_2:                      # @test_shrink_add_2
# BB#0:
	leaq	(%rdi,%rdx), %rax
	xorl	%edx, %edx
	retq
.Lfunc_end1:
	.size	test_shrink_add_2, .Lfunc_end1-test_shrink_add_2

	.globl	test_shrink_mul_1
	.align	16, 0x90
	.type	test_shrink_mul_1,@function
test_shrink_mul_1:                      # @test_shrink_mul_1
# BB#0:
	movq	%rdx, %rax
	mulq	%rdi
	retq
.Lfunc_end2:
	.size	test_shrink_mul_1, .Lfunc_end2-test_shrink_mul_1

	.globl	test_shrink_mul_2
	.align	16, 0x90
	.type	test_shrink_mul_2,@function
test_shrink_mul_2:                      # @test_shrink_mul_2
# BB#0:
	imulq	%rdx, %rdi
	xorl	%edx, %edx
	movq	%rdi, %rax
	retq
.Lfunc_end3:
	.size	test_shrink_mul_2, .Lfunc_end3-test_shrink_mul_2


	.section	".note.GNU-stack","",@progbits