[llvm] r296389 - [ARM] don't transform an add(ext Cond), C to select unless there's a setcc of the condition

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Mon Feb 27 15:30:54 2017
New Revision: 296389

URL: http://llvm.org/viewvc/llvm-project?rev=296389&view=rev
Log:
[ARM] don't transform an add(ext Cond), C to select unless there's a setcc of the condition

The transform in question claims to be doing:

// fold (add (select cc, 0, c), x) -> (select cc, x, (add, x, c))

...starting in PerformADDCombineWithOperands(), but it wasn't actually checking for a setcc node
for the sext/zext patterns.

This is exactly the opposite of a transform I'd like to add to DAGCombiner's foldSelectOfConstants(),
so I was seeing infinite loops with my draft of a patch applied.

The changes in select_const.ll look positive (less instructions). The change in arm-and-tst-peephole.ll
is unrelated. We're changing the input IR in that test to preserve the intent of the test, but that's 
not affected by this code change.

Differential Revision:
https://reviews.llvm.org/D30355


Modified:
    llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
    llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll
    llvm/trunk/test/CodeGen/ARM/select_const.ll

Modified: llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp?rev=296389&r1=296388&r2=296389&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp Mon Feb 27 15:30:54 2017
@@ -9163,7 +9163,7 @@ static bool isConditionalZeroOrAllOnes(S
     SDLoc dl(N);
     EVT VT = N->getValueType(0);
     CC = N->getOperand(0);
-    if (CC.getValueType() != MVT::i1)
+    if (CC.getValueType() != MVT::i1 || CC.getOpcode() != ISD::SETCC)
       return false;
     Invert = !AllOnes;
     if (AllOnes)

Modified: llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll?rev=296389&r1=296388&r2=296389&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/arm-and-tst-peephole.ll Mon Feb 27 15:30:54 2017
@@ -140,7 +140,7 @@ return:
 ; folding of unrelated tests (in this case, a TST against r1 was eliminated in
 ; favour of an AND of r0).
 
-define i32 @test_tst_assessment(i1 %lhs, i1 %rhs) {
+define i32 @test_tst_assessment(i32 %a, i32 %b) {
 ; ARM-LABEL: test_tst_assessment:
 ; ARM:       @ BB#0:
 ; ARM-NEXT:    and r0, r0, #1
@@ -150,11 +150,13 @@ define i32 @test_tst_assessment(i1 %lhs,
 ;
 ; THUMB-LABEL: test_tst_assessment:
 ; THUMB:       @ BB#0:
-; THUMB-NEXT:    movs r2, #1
-; THUMB-NEXT:    ands r2, r0
-; THUMB-NEXT:    subs r0, r2, #1
+; THUMB-NEXT:    push {r0}
+; THUMB-NEXT:    pop {r2}
+; THUMB-NEXT:    movs r0, #1
+; THUMB-NEXT:    ands r0, r2
+; THUMB-NEXT:    subs r2, r0, #1
 ; THUMB-NEXT:    lsls r1, r1, #31
-; THUMB-NEXT:    bne .LBB2_2
+; THUMB-NEXT:    beq .LBB2_2
 ; THUMB-NEXT:  @ BB#1:
 ; THUMB-NEXT:    push {r2}
 ; THUMB-NEXT:    pop {r0}
@@ -176,10 +178,12 @@ define i32 @test_tst_assessment(i1 %lhs,
 ; V8-NEXT:    it ne
 ; V8-NEXT:    subne r0, #1
 ; V8-NEXT:    bx lr
-  %lhs32 = zext i1 %lhs to i32
-  %rhs32 = zext i1 %rhs to i32
-  %diff = sub nsw i32 %lhs32, %rhs32
-  ret i32 %diff
+  %and1 = and i32 %a, 1
+  %sub = sub i32 %and1, 1
+  %and2 = and i32 %b, 1
+  %cmp = icmp eq i32 %and2, 0
+  %sel = select i1 %cmp, i32 %and1, i32 %sub
+  ret i32 %sel
 }
 
 !1 = !{!"branch_weights", i32 1, i32 1, i32 3, i32 2 }

Modified: llvm/trunk/test/CodeGen/ARM/select_const.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/select_const.ll?rev=296389&r1=296388&r2=296389&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/select_const.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/select_const.ll Mon Feb 27 15:30:54 2017
@@ -98,9 +98,8 @@ define i32 @select_0_or_neg1_signext(i1
 define i32 @select_0_or_neg1_alt(i1 %cond) {
 ; CHECK-LABEL: select_0_or_neg1_alt:
 ; CHECK:       @ BB#0:
-; CHECK-NEXT:    mov r1, #1
-; CHECK-NEXT:    bic r0, r1, r0
-; CHECK-NEXT:    rsb r0, r0, #0
+; CHECK-NEXT:    and r0, r0, #1
+; CHECK-NEXT:    sub r0, r0, #1
 ; CHECK-NEXT:    mov pc, lr
   %z = zext i1 %cond to i32
   %add = add i32 %z, -1
@@ -110,8 +109,7 @@ define i32 @select_0_or_neg1_alt(i1 %con
 define i32 @select_0_or_neg1_alt_zeroext(i1 zeroext %cond) {
 ; CHECK-LABEL: select_0_or_neg1_alt_zeroext:
 ; CHECK:       @ BB#0:
-; CHECK-NEXT:    eor r0, r0, #1
-; CHECK-NEXT:    rsb r0, r0, #0
+; CHECK-NEXT:    sub r0, r0, #1
 ; CHECK-NEXT:    mov pc, lr
   %z = zext i1 %cond to i32
   %add = add i32 %z, -1