[RISCV] Improve use of BSETI/BCLRI in constant materialization.

[topperc]

We failed to use BSETI when bit 31 was set and a few bits above bit 31 were set. We also failed to use multiple BSETI when the low 32 bits were zero.

I've removed the special cases for constants 0x80000000-0xffffffff and wrote a more generic algorithm for BSETI.

I've rewritten the BCLRI handling to be similar to the new BSETI algorithm. This picks up cases where bit 31 is 0 and only a few high bits are 0.

[llvmbot]

@llvm/pr-subscribers-backend-risc-v

Author: Craig Topper (topperc)

Changes

We failed to use BSETI when bit 31 was set and a few bits above bit 31 were set. We also failed to use multiple BSETI when the low 32 bits were zero.

I've removed the special cases for constants 0x80000000-0xffffffff and wrote a more generic algorithm for BSETI.

I've rewritten the BCLRI handling to be similar to the new BSETI algorithm. I'm not sure if this adds any new cases we weren't handling before.

---

Full diff: https://github.com/llvm/llvm-project/pull/91546.diff

3 Files Affected:

• (modified) llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp (+36-44)
• (modified) llvm/test/CodeGen/RISCV/imm.ll (+4-6)
• (modified) llvm/test/CodeGen/RISCV/rv64-legal-i32/imm.ll (+4-6)

diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp
index c3bae152993ea..aaa76cab4e5ac 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMatInt.cpp
@@ -10,7 +10,9 @@
 #include "MCTargetDesc/RISCVMCTargetDesc.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/MC/MCInstBuilder.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 static int getInstSeqCost(RISCVMatInt::InstSeq &Res, bool HasRVC) {
@@ -310,56 +312,46 @@ InstSeq generateInstSeq(int64_t Val, const MCSubtargetInfo &STI) {
     }
   }
 
-  // Perform optimization with BCLRI/BSETI in the Zbs extension.
+  // Perform optimization with BSETI in the Zbs extension.
   if (Res.size() > 2 && STI.hasFeature(RISCV::FeatureStdExtZbs)) {
-    // 1. For values in range 0xffffffff 7fffffff ~ 0xffffffff 00000000,
-    //    call generateInstSeqImpl with Val|0x80000000 (which is expected be
-    //    an int32), then emit (BCLRI r, 31).
-    // 2. For values in range 0x80000000 ~ 0xffffffff, call generateInstSeqImpl
-    //    with Val&~0x80000000 (which is expected to be an int32), then
-    //    emit (BSETI r, 31).
-    int64_t NewVal;
-    unsigned Opc;
-    if (Val < 0) {
-      Opc = RISCV::BCLRI;
-      NewVal = Val | 0x80000000ll;
-    } else {
-      Opc = RISCV::BSETI;
-      NewVal = Val & ~0x80000000ll;
-    }
-    if (isInt<32>(NewVal)) {
-      RISCVMatInt::InstSeq TmpSeq;
-      generateInstSeqImpl(NewVal, STI, TmpSeq);
-      if ((TmpSeq.size() + 1) < Res.size()) {
-        TmpSeq.emplace_back(Opc, 31);
-        Res = TmpSeq;
-      }
+    // Create a simm32 value for LUI+ADDIW with by forcing the upper 33 bits to
+    // zero. Xor that with original value to get which bits need to be set by
+    // BSETI.
+    uint64_t Lo = Val & 0x7fffffff;
+    uint64_t Hi = Val ^ Lo;
+    assert(Hi != 0);
+    RISCVMatInt::InstSeq TmpSeq;
+
+    if (Lo != 0)
+      generateInstSeqImpl(Lo, STI, TmpSeq);
+
+    if (TmpSeq.size() + llvm::popcount(Hi) < Res.size()) {
+      do {
+        TmpSeq.emplace_back(RISCV::BSETI, llvm::countr_zero(Hi));
+        Hi &= (Hi - 1); // Clear lowest set bit.
+      } while (Hi != 0);
+      Res = TmpSeq;
     }
+  }
+
+  // Perform optimization with BCLRI in the Zbs extension.
+  if (Res.size() > 2 && STI.hasFeature(RISCV::FeatureStdExtZbs)) {
+    // Create a simm32 value for LUI+ADDIW with by forcing the upper 33 bits to
+    // one. Xor that with original value to get which bits need to be cleared by
+    // BCLRI.
+    uint64_t Lo = Val | 0xffffffff80000000;
+    uint64_t Hi = Val ^ Lo;
+    assert(Hi != 0);
 
-    // Try to use BCLRI for upper 32 bits if the original lower 32 bits are
-    // negative int32, or use BSETI for upper 32 bits if the original lower
-    // 32 bits are positive int32.
-    int32_t Lo = Lo_32(Val);
-    uint32_t Hi = Hi_32(Val);
-    Opc = 0;
     RISCVMatInt::InstSeq TmpSeq;
     generateInstSeqImpl(Lo, STI, TmpSeq);
-    // Check if it is profitable to use BCLRI/BSETI.
-    if (Lo > 0 && TmpSeq.size() + llvm::popcount(Hi) < Res.size()) {
-      Opc = RISCV::BSETI;
-    } else if (Lo < 0 && TmpSeq.size() + llvm::popcount(~Hi) < Res.size()) {
-      Opc = RISCV::BCLRI;
-      Hi = ~Hi;
-    }
-    // Search for each bit and build corresponding BCLRI/BSETI.
-    if (Opc > 0) {
-      while (Hi != 0) {
-        unsigned Bit = llvm::countr_zero(Hi);
-        TmpSeq.emplace_back(Opc, Bit + 32);
+
+    if (TmpSeq.size() + llvm::popcount(Hi) < Res.size()) {
+      do {
+        TmpSeq.emplace_back(RISCV::BCLRI, llvm::countr_zero(Hi));
         Hi &= (Hi - 1); // Clear lowest set bit.
-      }
-      if (TmpSeq.size() < Res.size())
-        Res = TmpSeq;
+      } while (Hi != 0);
+      Res = TmpSeq;
     }
   }
 
diff --git a/llvm/test/CodeGen/RISCV/imm.ll b/llvm/test/CodeGen/RISCV/imm.ll
index 6456401dbb865..0f3c820939af5 100644
--- a/llvm/test/CodeGen/RISCV/imm.ll
+++ b/llvm/test/CodeGen/RISCV/imm.ll
@@ -4025,9 +4025,8 @@ define i64 @imm64_0x8000080000000() {
 ;
 ; RV64IZBS-LABEL: imm64_0x8000080000000:
 ; RV64IZBS:       # %bb.0:
-; RV64IZBS-NEXT:    lui a0, 256
-; RV64IZBS-NEXT:    addiw a0, a0, 1
-; RV64IZBS-NEXT:    slli a0, a0, 31
+; RV64IZBS-NEXT:    bseti a0, zero, 31
+; RV64IZBS-NEXT:    bseti a0, a0, 51
 ; RV64IZBS-NEXT:    ret
 ;
 ; RV64IXTHEADBB-LABEL: imm64_0x8000080000000:
@@ -4083,9 +4082,8 @@ define i64 @imm64_0x10000100000000() {
 ;
 ; RV64IZBS-LABEL: imm64_0x10000100000000:
 ; RV64IZBS:       # %bb.0:
-; RV64IZBS-NEXT:    lui a0, 256
-; RV64IZBS-NEXT:    addi a0, a0, 1
-; RV64IZBS-NEXT:    slli a0, a0, 32
+; RV64IZBS-NEXT:    bseti a0, zero, 32
+; RV64IZBS-NEXT:    bseti a0, a0, 52
 ; RV64IZBS-NEXT:    ret
 ;
 ; RV64IXTHEADBB-LABEL: imm64_0x10000100000000:
diff --git a/llvm/test/CodeGen/RISCV/rv64-legal-i32/imm.ll b/llvm/test/CodeGen/RISCV/rv64-legal-i32/imm.ll
index c5bb7289e448a..9430de61c515b 100644
--- a/llvm/test/CodeGen/RISCV/rv64-legal-i32/imm.ll
+++ b/llvm/test/CodeGen/RISCV/rv64-legal-i32/imm.ll
@@ -2648,9 +2648,8 @@ define i64 @imm64_0x8000080000000() {
 ;
 ; RV64IZBS-LABEL: imm64_0x8000080000000:
 ; RV64IZBS:       # %bb.0:
-; RV64IZBS-NEXT:    lui a0, 256
-; RV64IZBS-NEXT:    addiw a0, a0, 1
-; RV64IZBS-NEXT:    slli a0, a0, 31
+; RV64IZBS-NEXT:    bseti a0, zero, 31
+; RV64IZBS-NEXT:    bseti a0, a0, 51
 ; RV64IZBS-NEXT:    ret
 ;
 ; RV64IXTHEADBB-LABEL: imm64_0x8000080000000:
@@ -2686,9 +2685,8 @@ define i64 @imm64_0x10000100000000() {
 ;
 ; RV64IZBS-LABEL: imm64_0x10000100000000:
 ; RV64IZBS:       # %bb.0:
-; RV64IZBS-NEXT:    lui a0, 256
-; RV64IZBS-NEXT:    addi a0, a0, 1
-; RV64IZBS-NEXT:    slli a0, a0, 32
+; RV64IZBS-NEXT:    bseti a0, zero, 32
+; RV64IZBS-NEXT:    bseti a0, a0, 52
 ; RV64IZBS-NEXT:    ret
 ;
 ; RV64IXTHEADBB-LABEL: imm64_0x10000100000000:

[dtcxzyw]

LGTM. Thank you!

[dtcxzyw]

I don't think these header files are required.

[topperc]

They aren't. I was using them for debug printing and forgot to remove them