[InstCombine] Add new tests in preparation for a combine of icmp (mul nsw/nuw X, C2), C

[Nicola]

Summary

I'll also open a review for the new combine in InstCombine after this is submitted

Alive proofs for the combines I want to add:

ult/slt https://rise4fun.com/Alive/DJg
ugt/sgt https://rise4fun.com/Alive/2RBn
eq/ne   https://rise4fun.com/Alive/iUsl

[lebedev.ri]

Does this contain negative tests, that should not be folded?

[Nicola]

Added some negative tests

[spatel]

LGTM - the tests can be enhanced as we add/evolve the code for these folds.

I didn't look at all of the proofs, but at least for this pair, we can simplify the pre-conditions:
https://rise4fun.com/Alive/plgd

Also, for unsigned math, I think you want to use Alive's unsigned notation to match how the transforms will be coded:
https://rise4fun.com/Alive/nE9

Getting the pre-conditions right looks tricky, so I think it will be best to introduce the transforms for these 1 or 2 patterns at a time, so we can be sure we get each case right.

test/Transforms/InstCombine/icmp-mul.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; Tests for slt/ult
+
+define i1 @slt_positive_multip_rem_zero(i8 %x) {
+; CHECK-LABEL: @slt_positive_multip_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nsw i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp slt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nsw i8 %x, 7
+  %b = icmp slt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @slt_negative_multip_rem_zero(i8 %x) {
+; CHECK-LABEL: @slt_negative_multip_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nsw i8 [[X:%.*]], -7
+; CHECK-NEXT:    [[B:%.*]] = icmp slt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nsw i8 %x, -7
+  %b = icmp slt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @slt_positive_multip_rem_nz(i8 %x) {
+; CHECK-LABEL: @slt_positive_multip_rem_nz(
+; CHECK-NEXT:    [[A:%.*]] = mul nsw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp slt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nsw i8 %x, 5
+  %b = icmp slt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @ult_rem_zero(i8 %x) {
+; CHECK-LABEL: @ult_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp ult i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 7
+  %b = icmp ult i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @ult_rem_nz(i8 %x) {
+; CHECK-LABEL: @ult_rem_nz(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp ult i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 5
+  %b = icmp ult i8 %a, 21
+  ret i1 %b
+}
+
+; Tests for sgt/ugt
+
+define i1 @sgt_positive_multip_rem_zero(i8 %x) {
+; CHECK-LABEL: @sgt_positive_multip_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nsw i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp sgt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nsw i8 %x, 7
+  %b = icmp sgt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @sgt_negative_multip_rem_zero(i8 %x) {
+; CHECK-LABEL: @sgt_negative_multip_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nsw i8 [[X:%.*]], -7
+; CHECK-NEXT:    [[B:%.*]] = icmp sgt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nsw i8 %x, -7
+  %b = icmp sgt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @sgt_positive_multip_rem_nz(i8 %x) {
+; CHECK-LABEL: @sgt_positive_multip_rem_nz(
+; CHECK-NEXT:    [[A:%.*]] = mul nsw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp sgt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nsw i8 %x, 5
+  %b = icmp sgt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @ugt_rem_zero(i8 %x) {
+; CHECK-LABEL: @ugt_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp ugt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 7
+  %b = icmp ugt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @ugt_rem_nz(i8 %x) {
+; CHECK-LABEL: @ugt_rem_nz(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp ugt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 5
+  %b = icmp ugt i8 %a, 21
+  ret i1 %b
+}
+
+; Tests for eq/ne
+
+define i1 @eq_rem_zero(i8 %x) {
+; CHECK-LABEL: @eq_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i8 [[A]], 20
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 5
+  %b = icmp eq i8 %a, 20
+  ret i1 %b
+}
+
+define i1 @ne_rem_zero(i8 %x) {
+; CHECK-LABEL: @ne_rem_zero(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp ne i8 [[A]], 30
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 5
+  %b = icmp ne i8 %a, 30
+  ret i1 %b
+}
+
+define i1 @eq_rem_nz(i8 %x) {
+; CHECK-LABEL: @eq_rem_nz(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i8 [[A]], 31
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 5
+  %b = icmp eq i8 %a, 31
+  ret i1 %b
+}
+
+define i1 @ne_rem_nz(i8 %x) {
+; CHECK-LABEL: @ne_rem_nz(
+; CHECK-NEXT:    [[A:%.*]] = mul nuw i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp ne i8 [[A]], 31
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nuw i8 %x, 5
+  %b = icmp ne i8 %a, 31
+  ret i1 %b
+}
+
+; Negative tests for the icmp mul folds
+
+define i1 @sgt_positive_multip_rem_zero_nonsw(i8 %x) {
+; CHECK-LABEL: @sgt_positive_multip_rem_zero_nonsw(
+; CHECK-NEXT:    [[A:%.*]] = mul i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp sgt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul i8 %x, 7
+  %b = icmp sgt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @ult_multip_rem_zero_nonsw(i8 %x) {
+; CHECK-LABEL: @ult_multip_rem_zero_nonsw(
+; CHECK-NEXT:    [[A:%.*]] = mul i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp ult i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul i8 %x, 7
+  %b = icmp ult i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @ugt_rem_zero_nonuw(i8 %x) {
+; CHECK-LABEL: @ugt_rem_zero_nonuw(
+; CHECK-NEXT:    [[A:%.*]] = mul i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp ugt i8 [[A]], 21
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul i8 %x, 7
+  %b = icmp ugt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @sgt_minnum(i8 %x) {
+; CHECK-LABEL: @sgt_minnum(
+; CHECK-NEXT:    [[A:%.*]] = mul nsw i8 [[X:%.*]], 7
+; CHECK-NEXT:    [[B:%.*]] = icmp ne i8 [[A]], -128
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul nsw i8 %x, 7
+  %b = icmp sgt i8 %a, -128
+  ret i1 %b
+}
+
+define i1 @ule_bignum(i8 %x) {
+; CHECK-LABEL: @ule_bignum(
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i8 [[X:%.*]], 0
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul i8 %x, 2147483647
+  %b = icmp ule i8 %a, 0
+  ret i1 %b
+}
+
+define i1 @sgt_mulzero(i8 %x) {
+; CHECK-LABEL: @sgt_mulzero(
+; CHECK-NEXT:    ret i1 false
+;
+  %a = mul nsw i8 %x, 0
+  %b = icmp sgt i8 %a, 21
+  ret i1 %b
+}
+
+define i1 @eq_rem_zero_nonuw(i8 %x) {
+; CHECK-LABEL: @eq_rem_zero_nonuw(
+; CHECK-NEXT:    [[A:%.*]] = mul i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp eq i8 [[A]], 20
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul i8 %x, 5
+  %b = icmp eq i8 %a, 20
+  ret i1 %b
+}
+
+define i1 @ne_rem_zero_nonuw(i8 %x) {
+; CHECK-LABEL: @ne_rem_zero_nonuw(
+; CHECK-NEXT:    [[A:%.*]] = mul i8 [[X:%.*]], 5
+; CHECK-NEXT:    [[B:%.*]] = icmp ne i8 [[A]], 30
+; CHECK-NEXT:    ret i1 [[B]]
+;
+  %a = mul i8 %x, 5
+  %b = icmp ne i8 %a, 30
+  ret i1 %b
+}