[DAGCombiner] Improve shift by select of constant

laytonio · QingShan Zhang · commit 385e9a2a047b · 2020-12-18T02:21:42.000Z
Clean up a TODO, to support folding a shift of a constant by a select of constants, on targets with different shift operand sizes. Reviewed By: RKSimon, lebedev.ri Differential Revision: https://reviews.llvm.org/D90349
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2150,16 +2150,7 @@ SDValue DAGCombiner::foldBinOpIntoSelect(SDNode *BO) {
       !isConstantFPBuildVectorOrConstantFP(CBO))
     return SDValue();
 
-  EVT VT = Sel.getValueType();
-
-  // In case of shift value and shift amount may have different VT. For instance
-  // on x86 shift amount is i8 regardles of LHS type. Bail out if we have
-  // swapped operands and value types do not match. NB: x86 is fine if operands
-  // are not swapped with shift amount VT being not bigger than shifted value.
-  // TODO: that is possible to check for a shift operation, correct VTs and
-  // still perform optimization on x86 if needed.
-  if (SelOpNo && VT != CBO.getValueType())
-    return SDValue();
+  EVT VT = BO->getValueType(0);
 
   // We have a select-of-constants followed by a binary operator with a
   // constant. Eliminate the binop by pulling the constant math into the select.
diff --git a/llvm/test/CodeGen/AArch64/select_const.ll b/llvm/test/CodeGen/AArch64/select_const.ll
@@ -437,10 +437,9 @@ define i8 @shl_constant_sel_constants(i1 %cond) {
 ; CHECK-LABEL: shl_constant_sel_constants:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    tst w0, #0x1
-; CHECK-NEXT:    mov w8, #2
-; CHECK-NEXT:    cinc x8, x8, eq
-; CHECK-NEXT:    mov w9, #1
-; CHECK-NEXT:    lsl w0, w9, w8
+; CHECK-NEXT:    mov w8, #8
+; CHECK-NEXT:    mov w9, #4
+; CHECK-NEXT:    csel w0, w9, w8, ne
 ; CHECK-NEXT:    ret
   %sel = select i1 %cond, i8 2, i8 3
   %bo = shl i8 1, %sel
@@ -463,10 +462,9 @@ define i8 @lshr_constant_sel_constants(i1 %cond) {
 ; CHECK-LABEL: lshr_constant_sel_constants:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    tst w0, #0x1
-; CHECK-NEXT:    mov w8, #2
-; CHECK-NEXT:    cinc x8, x8, eq
-; CHECK-NEXT:    mov w9, #64
-; CHECK-NEXT:    lsr w0, w9, w8
+; CHECK-NEXT:    mov w8, #8
+; CHECK-NEXT:    mov w9, #16
+; CHECK-NEXT:    csel w0, w9, w8, ne
 ; CHECK-NEXT:    ret
   %sel = select i1 %cond, i8 2, i8 3
   %bo = lshr i8 64, %sel
@@ -488,10 +486,9 @@ define i8 @ashr_constant_sel_constants(i1 %cond) {
 ; CHECK-LABEL: ashr_constant_sel_constants:
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    tst w0, #0x1
-; CHECK-NEXT:    mov w8, #2
-; CHECK-NEXT:    cinc x8, x8, eq
-; CHECK-NEXT:    mov w9, #-128
-; CHECK-NEXT:    asr w0, w9, w8
+; CHECK-NEXT:    mov w8, #-16
+; CHECK-NEXT:    mov w9, #-32
+; CHECK-NEXT:    csel w0, w9, w8, ne
 ; CHECK-NEXT:    ret
   %sel = select i1 %cond, i8 2, i8 3
   %bo = ashr i8 128, %sel
diff --git a/llvm/test/CodeGen/PowerPC/select_const.ll b/llvm/test/CodeGen/PowerPC/select_const.ll
@@ -610,13 +610,24 @@ define i8 @sel_constants_shl_constant(i1 %cond) {
 }
 
 define i8 @shl_constant_sel_constants(i1 %cond) {
-; ALL-LABEL: shl_constant_sel_constants:
-; ALL:       # %bb.0:
-; ALL-NEXT:    clrlwi 3, 3, 31
-; ALL-NEXT:    li 4, 1
-; ALL-NEXT:    subfic 3, 3, 3
-; ALL-NEXT:    slw 3, 4, 3
-; ALL-NEXT:    blr
+; ISEL-LABEL: shl_constant_sel_constants:
+; ISEL:       # %bb.0:
+; ISEL-NEXT:    andi. 3, 3, 1
+; ISEL-NEXT:    li 4, 4
+; ISEL-NEXT:    li 3, 8
+; ISEL-NEXT:    iselgt 3, 4, 3
+; ISEL-NEXT:    blr
+;
+; NO_ISEL-LABEL: shl_constant_sel_constants:
+; NO_ISEL:       # %bb.0:
+; NO_ISEL-NEXT:    andi. 3, 3, 1
+; NO_ISEL-NEXT:    li 4, 4
+; NO_ISEL-NEXT:    li 3, 8
+; NO_ISEL-NEXT:    bc 12, 1, .LBB37_1
+; NO_ISEL-NEXT:    blr
+; NO_ISEL-NEXT:  .LBB37_1:
+; NO_ISEL-NEXT:    addi 3, 4, 0
+; NO_ISEL-NEXT:    blr
   %sel = select i1 %cond, i8 2, i8 3
   %bo = shl i8 1, %sel
   ret i8 %bo
@@ -647,13 +658,24 @@ define i8 @sel_constants_lshr_constant(i1 %cond) {
 }
 
 define i8 @lshr_constant_sel_constants(i1 %cond) {
-; ALL-LABEL: lshr_constant_sel_constants:
-; ALL:       # %bb.0:
-; ALL-NEXT:    clrlwi 3, 3, 31
-; ALL-NEXT:    li 4, 64
-; ALL-NEXT:    subfic 3, 3, 3
-; ALL-NEXT:    srw 3, 4, 3
-; ALL-NEXT:    blr
+; ISEL-LABEL: lshr_constant_sel_constants:
+; ISEL:       # %bb.0:
+; ISEL-NEXT:    andi. 3, 3, 1
+; ISEL-NEXT:    li 4, 16
+; ISEL-NEXT:    li 3, 8
+; ISEL-NEXT:    iselgt 3, 4, 3
+; ISEL-NEXT:    blr
+;
+; NO_ISEL-LABEL: lshr_constant_sel_constants:
+; NO_ISEL:       # %bb.0:
+; NO_ISEL-NEXT:    andi. 3, 3, 1
+; NO_ISEL-NEXT:    li 4, 16
+; NO_ISEL-NEXT:    li 3, 8
+; NO_ISEL-NEXT:    bc 12, 1, .LBB39_1
+; NO_ISEL-NEXT:    blr
+; NO_ISEL-NEXT:  .LBB39_1:
+; NO_ISEL-NEXT:    addi 3, 4, 0
+; NO_ISEL-NEXT:    blr
   %sel = select i1 %cond, i8 2, i8 3
   %bo = lshr i8 64, %sel
   ret i8 %bo
@@ -672,13 +694,24 @@ define i8 @sel_constants_ashr_constant(i1 %cond) {
 }
 
 define i8 @ashr_constant_sel_constants(i1 %cond) {
-; ALL-LABEL: ashr_constant_sel_constants:
-; ALL:       # %bb.0:
-; ALL-NEXT:    clrlwi 3, 3, 31
-; ALL-NEXT:    li 4, -128
-; ALL-NEXT:    subfic 3, 3, 3
-; ALL-NEXT:    sraw 3, 4, 3
-; ALL-NEXT:    blr
+; ISEL-LABEL: ashr_constant_sel_constants:
+; ISEL:       # %bb.0:
+; ISEL-NEXT:    andi. 3, 3, 1
+; ISEL-NEXT:    li 4, -32
+; ISEL-NEXT:    li 3, -16
+; ISEL-NEXT:    iselgt 3, 4, 3
+; ISEL-NEXT:    blr
+;
+; NO_ISEL-LABEL: ashr_constant_sel_constants:
+; NO_ISEL:       # %bb.0:
+; NO_ISEL-NEXT:    andi. 3, 3, 1
+; NO_ISEL-NEXT:    li 4, -32
+; NO_ISEL-NEXT:    li 3, -16
+; NO_ISEL-NEXT:    bc 12, 1, .LBB41_1
+; NO_ISEL-NEXT:    blr
+; NO_ISEL-NEXT:  .LBB41_1:
+; NO_ISEL-NEXT:    addi 3, 4, 0
+; NO_ISEL-NEXT:    blr
   %sel = select i1 %cond, i8 2, i8 3
   %bo = ashr i8 128, %sel
   ret i8 %bo
diff --git a/llvm/test/CodeGen/X86/dagcombine-select.ll b/llvm/test/CodeGen/X86/dagcombine-select.ll
@@ -194,12 +194,10 @@ define i32 @sel_constants_shl_constant(i1 %cond) {
 define i32 @shl_constant_sel_constants(i1 %cond) {
 ; CHECK-LABEL: shl_constant_sel_constants:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    movl %edi, %ecx
-; CHECK-NEXT:    andb $1, %cl
-; CHECK-NEXT:    xorb $3, %cl
-; CHECK-NEXT:    movl $1, %eax
-; CHECK-NEXT:    # kill: def $cl killed $cl killed $ecx
-; CHECK-NEXT:    shll %cl, %eax
+; CHECK-NEXT:    notb %dil
+; CHECK-NEXT:    movzbl %dil, %eax
+; CHECK-NEXT:    andl $1, %eax
+; CHECK-NEXT:    leal 4(,%rax,4), %eax
 ; CHECK-NEXT:    retq
   %sel = select i1 %cond, i32 2, i32 3
   %bo = shl i32 1, %sel
@@ -209,12 +207,9 @@ define i32 @shl_constant_sel_constants(i1 %cond) {
 define i32 @lshr_constant_sel_constants(i1 %cond) {
 ; CHECK-LABEL: lshr_constant_sel_constants:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    movl %edi, %ecx
-; CHECK-NEXT:    andb $1, %cl
-; CHECK-NEXT:    xorb $3, %cl
-; CHECK-NEXT:    movl $64, %eax
-; CHECK-NEXT:    # kill: def $cl killed $cl killed $ecx
-; CHECK-NEXT:    shrl %cl, %eax
+; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
+; CHECK-NEXT:    andl $1, %edi
+; CHECK-NEXT:    leal 8(,%rdi,8), %eax
 ; CHECK-NEXT:    retq
   %sel = select i1 %cond, i32 2, i32 3
   %bo = lshr i32 64, %sel
@@ -224,12 +219,10 @@ define i32 @lshr_constant_sel_constants(i1 %cond) {
 define i32 @ashr_constant_sel_constants(i1 %cond) {
 ; CHECK-LABEL: ashr_constant_sel_constants:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    movl %edi, %ecx
-; CHECK-NEXT:    andb $1, %cl
-; CHECK-NEXT:    xorb $3, %cl
-; CHECK-NEXT:    movl $128, %eax
-; CHECK-NEXT:    # kill: def $cl killed $cl killed $ecx
-; CHECK-NEXT:    shrl %cl, %eax
+; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
+; CHECK-NEXT:    andl $1, %edi
+; CHECK-NEXT:    shll $4, %edi
+; CHECK-NEXT:    leal 16(%rdi), %eax
 ; CHECK-NEXT:    retq
   %sel = select i1 %cond, i32 2, i32 3
   %bo = ashr i32 128, %sel
