[SelectionDAG] Fix comment

Author: vfdff

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -17629,7 +17629,7 @@ static SDValue performMulCombine(SDNode *N, SelectionDAG &DAG,
     // (mul x, (2^M + 1) * 2^N + 1))
     //     =>  MV = add (shl x, M), x); add (shl MV, N), x)
     // (mul x, 1 - (1 - 2^M) * 2^N))
-    //     =>  MV = sub (x - (shl x, M)); add (x - (shl x, M))
+    //     =>  MV = sub (x - (shl x, M)); sub (x - (shl MV, N))
     APInt SCVMinus1 = ShiftedConstValue - 1;
     APInt SCVPlus1 = ShiftedConstValue + 1;
     APInt CVPlus1 = ConstValue + 1;

llvm/test/CodeGen/AArch64/mul_pow2.ll

@@ -646,11 +646,11 @@ define i32 @test125_fast_shift(i32 %x) "target-features"="+alu-lsl-fast" {
 ; GISEL-NEXT:    mul w0, w0, w8
 ; GISEL-NEXT:    ret
 
-  %mul = mul nsw i32 %x, 125 ; 63 = 1 - ((1-32) << 2)
+  %mul = mul nsw i32 %x, 125 ; 125 = 1 - ((1-32) << 2)
   ret i32 %mul
 }
 
-; Negative test: The shift number 5 is out of bound
+; TODO: (1 - 2^M) * (1 - 2^N)
 define i32 @test225_fast_shift(i32 %x) "target-features"="+alu-lsl-fast" {
 ; CHECK-LABEL: test225_fast_shift:
 ; CHECK:       // %bb.0:
@@ -664,7 +664,7 @@ define i32 @test225_fast_shift(i32 %x) "target-features"="+alu-lsl-fast" {
 ; GISEL-NEXT:    mul w0, w0, w8
 ; GISEL-NEXT:    ret
 
-  %mul = mul nsw i32 %x, 225 ; 225 = 1 - ((1-8) << 5)
+  %mul = mul nsw i32 %x, 225 ; 225 = (1-16)*(1-16)
   ret i32 %mul
 }
 
@@ -686,6 +686,24 @@ define i32 @test297_fast_shift(i32 %x) "target-features"="+alu-lsl-fast" {
   ret i32 %mul
 }
 
+; Negative test: The shift number 5 is out of bound
+define i32 @test481_fast_shift(i32 %x) "target-features"="+alu-lsl-fast" {
+; CHECK-LABEL: test481_fast_shift:
+; CHECK:       // %bb.0:
+; CHECK-NEXT:    mov w8, #481 // =0x1e1
+; CHECK-NEXT:    mul w0, w0, w8
+; CHECK-NEXT:    ret
+;
+; GISEL-LABEL: test481_fast_shift:
+; GISEL:       // %bb.0:
+; GISEL-NEXT:    mov w8, #481 // =0x1e1
+; GISEL-NEXT:    mul w0, w0, w8
+; GISEL-NEXT:    ret
+
+  %mul = mul nsw i32 %x, 481 ; 481 = 1 - ((1-16) << 5)
+  ret i32 %mul
+}
+
 ; Convert mul x, -pow2 to shift.
 ; Convert mul x, -(pow2 +/- 1) to shift + add/sub.
 ; Lowering other negative constants are not supported yet.
@@ -963,9 +981,9 @@ define <4 x i32> @muladd_demand_commute(<4 x i32> %x, <4 x i32> %y) {
 ;
 ; GISEL-LABEL: muladd_demand_commute:
 ; GISEL:       // %bb.0:
-; GISEL-NEXT:    adrp x8, .LCPI55_0
+; GISEL-NEXT:    adrp x8, .LCPI56_0
 ; GISEL-NEXT:    movi v3.4s, #1, msl #16
-; GISEL-NEXT:    ldr q2, [x8, :lo12:.LCPI55_0]
+; GISEL-NEXT:    ldr q2, [x8, :lo12:.LCPI56_0]
 ; GISEL-NEXT:    mla v1.4s, v0.4s, v2.4s
 ; GISEL-NEXT:    and v0.16b, v1.16b, v3.16b
 ; GISEL-NEXT:    ret