[InstCombine] Sink sub into hands of select if one hand becomes zero. Part 2 (PR44426)

This decreases use count of %Op0, makes one hand of select to be 0,
and possibly exposes further folding potential.

Name: sub %Op0, (select %Cond, %Op0, %FalseVal) -> select %Cond, 0, (sub %Op0, %FalseVal)
  %Op0 = %TrueVal
  %o = select i1 %Cond, i8 %Op0, i8 %FalseVal
  %r = sub i8 %Op0, %o
=>
  %n = sub i8 %Op0, %FalseVal
  %r = select i1 %Cond, i8 0, i8 %n

Name: sub %Op0, (select %Cond, %TrueVal, %Op0) -> select %Cond, (sub %Op0, %TrueVal), 0
  %Op0 = %FalseVal
  %o = select i1 %Cond, i8 %TrueVal, i8 %Op0
  %r = sub i8 %Op0, %o
=>
  %n = sub i8 %Op0, %TrueVal
  %r = select i1 %Cond, i8 %n, i8 0

https://rise4fun.com/Alive/aHRt

https://bugs.llvm.org/show_bug.cgi?id=44426

2 files changed, 16 insertions, 22 deletions

diff --git a/llvm/test/Transforms/InstCombine/sub-minmax.ll b/llvm/test/Transforms/InstCombine/sub-minmax.ll
index 7fb5e31d81e..58edf37195f 100644
--- a/llvm/test/Transforms/InstCombine/sub-minmax.ll
+++ b/llvm/test/Transforms/InstCombine/sub-minmax.ll
@@ -18,10 +18,8 @@ define i32 @max_na_b_minux_na(i32 %A, i32 %B) {
 define i32 @na_minus_max_na_b(i32 %A, i32 %B) {
 ; CHECK-LABEL: @na_minus_max_na_b(
 ; CHECK-NEXT:    [[NOT:%.*]] = xor i32 [[A:%.*]], -1
-; CHECK-NEXT:    [[L0:%.*]] = icmp ult i32 [[NOT]], [[B:%.*]]
-; CHECK-NEXT:    [[L1:%.*]] = select i1 [[L0]], i32 [[NOT]], i32 [[B]]
-; CHECK-NEXT:    [[X:%.*]] = sub i32 [[NOT]], [[L1]]
-; CHECK-NEXT:    ret i32 [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[NOT]], i32 [[B:%.*]])
+; CHECK-NEXT:    ret i32 [[TMP1]]
 ;
   %not = xor i32 %A, -1
   %l0 = icmp ult i32 %not, %B
@@ -47,10 +45,8 @@ define i32 @max_b_na_minus_na(i32 %A, i32 %B) {
 define i32 @na_minus_max_b_na(i32 %A, i32 %B) {
 ; CHECK-LABEL: @na_minus_max_b_na(
 ; CHECK-NEXT:    [[NOT:%.*]] = xor i32 [[A:%.*]], -1
-; CHECK-NEXT:    [[L0:%.*]] = icmp ugt i32 [[NOT]], [[B:%.*]]
-; CHECK-NEXT:    [[L1:%.*]] = select i1 [[L0]], i32 [[B]], i32 [[NOT]]
-; CHECK-NEXT:    [[X:%.*]] = sub i32 [[NOT]], [[L1]]
-; CHECK-NEXT:    ret i32 [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[NOT]], i32 [[B:%.*]])
+; CHECK-NEXT:    ret i32 [[TMP1]]
 ;
   %not = xor i32 %A, -1
   %l0 = icmp ugt i32 %not, %B
@@ -62,10 +58,9 @@ define i32 @na_minus_max_b_na(i32 %A, i32 %B) {
 
 define i32 @max_na_bi_minux_na(i32 %A, i32 %Bi) {
 ; CHECK-LABEL: @max_na_bi_minux_na(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i32 [[A:%.*]], [[BI:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[BI]], i32 [[A]]
-; CHECK-NEXT:    [[X:%.*]] = sub i32 [[A]], [[TMP2]]
-; CHECK-NEXT:    ret i32 [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[BI:%.*]], i32 [[A:%.*]])
+; CHECK-NEXT:    [[TMP2:%.*]] = sub i32 0, [[TMP1]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %B =  xor i32 %Bi, -1
   %not = xor i32 %A, -1
@@ -90,10 +85,9 @@ define i32 @na_minus_max_na_bi(i32 %A, i32 %Bi) {
 
 define i32 @max_bi_na_minus_na(i32 %A, i32 %Bi) {
 ; CHECK-LABEL: @max_bi_na_minus_na(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i32 [[A:%.*]], [[BI:%.*]]
-; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i32 [[BI]], i32 [[A]]
-; CHECK-NEXT:    [[X:%.*]] = sub i32 [[A]], [[TMP2]]
-; CHECK-NEXT:    ret i32 [[X]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[BI:%.*]], i32 [[A:%.*]])
+; CHECK-NEXT:    [[TMP2:%.*]] = sub i32 0, [[TMP1]]
+; CHECK-NEXT:    ret i32 [[TMP2]]
 ;
   %B =  xor i32 %Bi, -1
   %not = xor i32 %A, -1
diff --git a/llvm/test/Transforms/InstCombine/subtract-from-one-hand-of-select.ll b/llvm/test/Transforms/InstCombine/subtract-from-one-hand-of-select.ll
index 1e68efa8bc5..8ff2e0ee211 100644
--- a/llvm/test/Transforms/InstCombine/subtract-from-one-hand-of-select.ll
+++ b/llvm/test/Transforms/InstCombine/subtract-from-one-hand-of-select.ll
@@ -12,8 +12,8 @@
 
 define i8 @t0_sub_from_trueval(i1 %c, i8 %Op0, i8 %FalseVal) {
 ; CHECK-LABEL: @t0_sub_from_trueval(
-; CHECK-NEXT:    [[O:%.*]] = select i1 [[C:%.*]], i8 [[OP0:%.*]], i8 [[FALSEVAL:%.*]], !prof !0
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[OP0]], [[O]]
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i8 [[OP0:%.*]], [[FALSEVAL:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[C:%.*]], i8 0, i8 [[TMP1]], !prof !0
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %o = select i1 %c, i8 %Op0, i8 %FalseVal, !prof !0 ; while there, ensure preservation of prof md
@@ -22,8 +22,8 @@ define i8 @t0_sub_from_trueval(i1 %c, i8 %Op0, i8 %FalseVal) {
 }
 define i8 @t1_sub_from_falseval(i1 %c, i8 %TrueVal, i8 %Op0) {
 ; CHECK-LABEL: @t1_sub_from_falseval(
-; CHECK-NEXT:    [[O:%.*]] = select i1 [[C:%.*]], i8 [[TRUEVAL:%.*]], i8 [[OP0:%.*]], !prof !0
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[OP0]], [[O]]
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i8 [[OP0:%.*]], [[TRUEVAL:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[C:%.*]], i8 [[TMP1]], i8 0, !prof !0
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %o = select i1 %c, i8 %TrueVal, i8 %Op0, !prof !0 ; while there, ensure preservation of prof md
@@ -35,8 +35,8 @@ define i8 @t1_sub_from_falseval(i1 %c, i8 %TrueVal, i8 %Op0) {
 
 define <2 x i8> @t2_vec(i1 %c, <2 x i8> %Op0, <2 x i8> %FalseVal) {
 ; CHECK-LABEL: @t2_vec(
-; CHECK-NEXT:    [[O:%.*]] = select i1 [[C:%.*]], <2 x i8> [[OP0:%.*]], <2 x i8> [[FALSEVAL:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = sub <2 x i8> [[OP0]], [[O]]
+; CHECK-NEXT:    [[TMP1:%.*]] = sub <2 x i8> [[OP0:%.*]], [[FALSEVAL:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[C:%.*]], <2 x i8> zeroinitializer, <2 x i8> [[TMP1]]
 ; CHECK-NEXT:    ret <2 x i8> [[R]]
 ;
   %o = select i1 %c, <2 x i8> %Op0, <2 x i8> %FalseVal