[RISCV] Remove one bit of mantissa in RISCVLoadFPImm related code.

We only need 2 bits of mantissa. The third bit was always 0.

Author: topperc

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.cpp

@@ -216,21 +216,21 @@ bool RISCVRVC::uncompress(MCInst &OutInst, const MCInst &MI,
 
 // We expect an 5-bit binary encoding of a floating-point constant here.
 static constexpr std::pair<uint8_t, uint8_t> LoadFPImmArr[] = {
-    {0b00000001, 0b000}, {0b01101111, 0b000}, {0b01110000, 0b000},
-    {0b01110111, 0b000}, {0b01111000, 0b000}, {0b01111011, 0b000},
-    {0b01111100, 0b000}, {0b01111101, 0b000}, {0b01111101, 0b010},
-    {0b01111101, 0b100}, {0b01111101, 0b110}, {0b01111110, 0b000},
-    {0b01111110, 0b010}, {0b01111110, 0b100}, {0b01111110, 0b110},
-    {0b01111111, 0b000}, {0b01111111, 0b010}, {0b01111111, 0b100},
-    {0b01111111, 0b110}, {0b10000000, 0b000}, {0b10000000, 0b010},
-    {0b10000000, 0b100}, {0b10000001, 0b000}, {0b10000010, 0b000},
-    {0b10000011, 0b000}, {0b10000110, 0b000}, {0b10000111, 0b000},
-    {0b10001110, 0b000}, {0b10001111, 0b000}, {0b11111111, 0b000},
-    {0b11111111, 0b100},
+    {0b00000001, 0b00}, {0b01101111, 0b00}, {0b01110000, 0b00},
+    {0b01110111, 0b00}, {0b01111000, 0b00}, {0b01111011, 0b00},
+    {0b01111100, 0b00}, {0b01111101, 0b00}, {0b01111101, 0b01},
+    {0b01111101, 0b10}, {0b01111101, 0b11}, {0b01111110, 0b00},
+    {0b01111110, 0b01}, {0b01111110, 0b10}, {0b01111110, 0b11},
+    {0b01111111, 0b00}, {0b01111111, 0b01}, {0b01111111, 0b10},
+    {0b01111111, 0b11}, {0b10000000, 0b00}, {0b10000000, 0b01},
+    {0b10000000, 0b10}, {0b10000001, 0b00}, {0b10000010, 0b00},
+    {0b10000011, 0b00}, {0b10000110, 0b00}, {0b10000111, 0b00},
+    {0b10001110, 0b00}, {0b10001111, 0b00}, {0b11111111, 0b00},
+    {0b11111111, 0b10},
 };
 
 int RISCVLoadFPImm::getLoadFPImm(uint8_t Sign, uint8_t Exp, uint8_t Mantissa) {
-  if (Sign == 0b1 && Exp == 0b01111111 && Mantissa == 0b000)
+  if (Sign == 0b1 && Exp == 0b01111111 && Mantissa == 0b00)
     return 0;
 
   if (Sign == 0b0) {
@@ -252,14 +252,14 @@ float RISCVLoadFPImm::getFPImm(unsigned Imm) {
   if (Imm == 0) {
     Sign = 0b1;
     Exp = 0b01111111;
-    Mantissa = 0b000;
+    Mantissa = 0b00;
   } else {
     Sign = 0b0;
     Exp = LoadFPImmArr[Imm - 1].first;
     Mantissa = LoadFPImmArr[Imm - 1].second;
   }
 
-  uint32_t I = Sign << 31 | Exp << 23 | Mantissa << 20;
+  uint32_t I = Sign << 31 | Exp << 23 | Mantissa << 21;
   return bit_cast<float>(I);
 }
 

llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h

@@ -354,12 +354,12 @@ float getFPImm(unsigned Imm);
 /// floating-point immediate value. If the value cannot be represented as a
 /// 5-bit binary encoding, then return -1.
 static inline int getLoadFP32Imm(const APInt &Imm) {
-  if (Imm.extractBitsAsZExtValue(20, 0) != 0)
+  if (Imm.extractBitsAsZExtValue(21, 0) != 0)
     return -1;
 
   uint8_t Sign = Imm.extractBitsAsZExtValue(1, 31);
   uint8_t Exp = Imm.extractBitsAsZExtValue(8, 23);
-  uint8_t Mantissa = Imm.extractBitsAsZExtValue(3, 20);
+  uint8_t Mantissa = Imm.extractBitsAsZExtValue(2, 21);
   return getLoadFPImm(Sign, Exp, Mantissa);
 }
 
@@ -371,11 +371,11 @@ static inline int getLoadFP32Imm(const APFloat &FPImm) {
 /// floating-point immediate value. If the value cannot be represented as a
 /// 5-bit binary encoding, then return -1.
 static inline int getLoadFP64Imm(const APInt &Imm) {
-  if (Imm.extractBitsAsZExtValue(49, 0) != 0)
+  if (Imm.extractBitsAsZExtValue(50, 0) != 0)
     return -1;
 
   uint8_t Sign = Imm.extractBitsAsZExtValue(1, 63);
-  uint8_t Mantissa = Imm.extractBitsAsZExtValue(3, 49);
+  uint8_t Mantissa = Imm.extractBitsAsZExtValue(2, 50);
   uint8_t Exp;
   if (Imm.extractBitsAsZExtValue(11, 52) == 1)
     Exp = 0b00000001;
@@ -395,11 +395,11 @@ static inline int getLoadFP64Imm(const APFloat &FPImm) {
 /// floating-point immediate value. If the value cannot be represented as a
 /// 5-bit binary encoding, then return -1.
 static inline int getLoadFP16Imm(const APInt &Imm) {
-  if (Imm.extractBitsAsZExtValue(7, 0) != 0)
+  if (Imm.extractBitsAsZExtValue(8, 0) != 0)
     return -1;
 
   uint8_t Sign = Imm.extractBitsAsZExtValue(1, 15);
-  uint8_t Mantissa = Imm.extractBitsAsZExtValue(3, 7);
+  uint8_t Mantissa = Imm.extractBitsAsZExtValue(2, 8);
   uint8_t Exp;
   if (Imm.extractBitsAsZExtValue(5, 10) == 1)
     Exp = 0b00000001;